Author Archives: Michael Pfeifer, Ph.D., P.E.

About Michael Pfeifer, Ph.D., P.E.

Michael is Principal Engineer and Trainer at Industrial Metallurgists, LLC. Reach him at mike@imetllc.com or 847.528.3467

Materials Engineering and Successful Products

Successful product design and manufacturing requires the consideration of several perspectives including mechanical engineering, electrical engineering, materials engineering, manufacturing, sourcing, and supplier quality. This article discusses the materials engineering perspective for product design and manufacturing.  It is an abbreviated version of the first lesson in a free, 3-lesson series that teaches materials science and engineering as it applies to product design and manufacturing.

PropertiesDiagramMaterials Science and Engineering
Materials science is concerned with understanding the relationship between a material’s composition, microstructure, and properties and the effects of manufacturing processes and composition on a material’s microstructure. Materials engineering involves applying materials science knowledge to the engineering of products and manufacturing processes.

A collection of materials
An engineered product is a collection of materials in the shapes of components and weld, solder, or adhesive joints. In fact, up to 70% of the cost to make a product is due to its materials. Therefore, it makes sense that getting the materials right will have a big impact on a product’s success. However, many organizations have difficulties getting the materials right, and they end up facing common problems such as:

  • Materials that degrade too fast, resulting in premature product failure.
  • Components that cost too much.
  • Repeating product verification tests because sub-optimum materials fail
  • Suppliers incapable of providing materials and components that consistently meet requirements
  • Difficult to fabricate components and joints.

Many of these problems can be avoided by applying the materials engineering perspective to product design and manufacturing decisions.

ScissorsMaterials, not just components
What do you see here? A pair of scissors? Sharp metal blades and plastic handles? As a materials engineer, here’s what I see:

  • Two pieces of metal with the composition and microstructure necessary for the blades to have good corrosion resistance, high hardness to maintain the cutting edge, and good toughness so as not to fracture when dropped on concrete.
  • Plastic with the composition and microstructure necessary for the handles to be rigid enough to transfer a user’s force to the blades, and with enough strength and toughness so that they do not crack or break when the scissors are dropped onto a hard surface.

Furthermore, people will not buy the scissors or it will cost too much to manufacture if the blade or handle materials do not meet these requirements. The same concept applies to any product.

Meeting product performance, reliability, and cost requirements
PyramidProduct performance, reliability, and cost depends on component and joint performance, reliability, and cost, which depends on component and joint mechanical construction and the materials used for a component or joint. Mechanical construction refers to the shape, dimensions, and features of a component or joint.

Focusing on the materials used for components and joints, designing and manufacturing a successful product requires two things:

  1. Selecting materials that satisfy component and joint performance, reliability, and cost requirements.
  2. Implementing control measures that ensure the properties of materials that make up components and joints consistently meet specifications.

Whether a product meets all its performance, reliability, and cost requirements depends on whether a design team selects the appropriate materials. The process of selecting materials is discussed in the Materials Selection lesson of the series.

Controlling the variation of the properties of the materials used in a product requires

  • Writing thorough design and process specifications that list all pertinent materials requirements such as composition, microstructure, and properties.
  • A robust process for selecting suppliers capable of consistently providing materials that meet  requirements for composition, microstructure, and properties.
  • Using capable manufacturing and assembly processes.

Materials Enabled Designs
In conclusion, including the materials engineering perspective as part of product design and manufacturing enables selection of materials that have been optimized to meet performance, reliability, and cost requirements and control over the variation of the composition, microstructure, and properties of the materials so that they consistently meet their specifications. When both of these happen, the likelihood of product success is greatly improved.

If you’re interested in learning more, considering signing-up for the free, 3-lesson series that teaches materials science and engineering as it applies to product design and manufacturing

Cracked Chuck Failure Analysis

cracked chuck failure analysis

Problem
Determine the root cause of a tool chuck that was cracking during product assembly.

Description
About 30% of the tool chucks were cracking. The chuck was made of a stainless steel alloy that was similar to PH 13-8 Mo.  The component was fabricated from wire stock that had been 70% cold drawn.  The following fabrication processes were used to make the chuck:

  1. Machine hole through wire center
  2. Machine other features inside the hole
  3. Machine a slot into the side of the chuck
  4. Heat treat at 900 °F to precipitation age the steel to a final hardness of >53 Rockwell C, which was the peak hardness of the steel.

The cracks initiated at the root of the slot when a mating part was inserted into the chuck.

Analysis
To start the failure analysis, cracked samples were split open completely to allow the fracture surface to be examined with a scanning electron microscope. The analysis indicated that the fracture mode was dimple rupture, indicating that the metal was exposed to a stress that exceeded its tensile strength.  However, there was no plastic deformation of the material around the crack, which indicated that the metal had very little ductility.

Solve Failures Faster b

The heat treatment that was used resulted in a steel with high yield and tensile strength and poor fracture toughness.  Using a higher heat treating temperature of 1000 or 1050 °F was recommended.  This heat treatment resulted in overaging, with a slight reduction in strength, but almost double the fracture toughness.  The reduction in strength was acceptable, so the recommendation was implemented, and the cracking no longer occurred.

Conclusions
The root cause of the cracking was poor design.  The heat treatment that was specified resulted in a material that had poor fracture toughness.

Could the problem have been prevented?
Yes.  Completing a failure modes and effects analysis (FMEA) when the product was being designed would have probably identified cracking as a potential failure mode.  An FMEA involves reviewing components, assemblies, and subsystems to identify failure modes, and their causes and effects. For each component, the failure modes and their resulting effects on the rest of the system are recorded in an FMEA worksheet.  There are both design and process (Manufacturing and Assembly) FMEA analyses.

A successful FMEA activity helps to identify potential failure modes based on experience with similar products and processes – or based on common physics of failure logic. It is widely used in development and manufacturing industries in various phases of the product life cycle.

Learn the Principles Banner Ad

While performing an FMEA can be laborious, the output is often very powerful for giving design and manufacturing teams clear direction on engineering issues to resolve during product design and manufacturing process development.  Ultimately, the impact is improved product reliability, more capable manufacturing and assembly process reliability, and fewer problems and surprises.

Had the design team for the product considered here performed a design FMEA, they may have identified the susceptibility of the chuck to cracking, and considered an analysis of the effects of different aging heat treatments on the cracking.  With this information, the design team could have optimized the mechanical design and metal properties requirements.

Information about how to perform an FMEAs is available in the publication “Potential Failure Mode & Effects Analysis”, which is available from AIAG at www.aiag.org.

Case Study: Material Selection for Drive Shaft

ShaftCrossSection

Drive shaft cross section

Project
Select the material to use for a 1/2-inch diameter, six foot long drive shaft used to run a power tool attached to one end of a pole assembly.  The drive shaft  cross-section is shown here.

Description
The main requirements for the shaft material were:

  • Yield strength > 30 ksi
  • 5 years before failure – corresponds to 3,500 hours actual use
  • Lightweight
  • Easy to manufacture
  • Corrosion resistant

Based on these requirements, only aluminum alloys were considered.  Steel alloys were not considered because of their weight.  Copper alloys were not considered because of their weight and cost.  Though plastics were available that met the yield strength requirement, there was concern about the ability to obtain uniform properties in the small shaft splines.

The most cost effective option to consider was extruded 6061 aluminum in a T6 temper condition. The Aluminum Association specification for 6061-T6 requires a minimum yield strength of 35 ksi.  6061 is a commonly extruded alloy that is less expensive to purchase and easy to extrude compared to other aluminum alloys that meet the strength requirement.

Material Evaluation Process
Part of selecting a material to use for a component involves the following steps:

  • Evaluating prototypes to determine whether the material can meet the application performance and reliability requirements.
  • Evaluating potential suppliers of the component to determine whether they are capable of producing components that meet the specifications.

Evaluating Prototypes
Prototype evaluation involved machining 6061-T6 rod stock into shaft samples.  Samples were tested using accelerated test conditions to simulate 3,500 hours use.  Two other aluminum alloys that had higher yield strength than 6061-T6 were also evaluated, just in case testing indicated that options were required.  The testing revealed that minor changes in the shaft cross-section dimensions were required to prevent failure before 3,500 hours.  Also, it was determined that 6061-T6 was suitable.  Since tooling for the shaft had not begun, the dimension changes were easy to make.

Supplier Evaluation
Evaluating suppliers did not require obtaining samples of the shaft, which was a good thing because the tooling needed to make the shaft would not have been ready until later in the development cycle.  Production samples of extruded 6061-T6 components that were similar to the shaft were obtained from two extrusion companies and were evaluated to see whether they met the composition and strength requirements for 6061-T6.  Metallographic examination of one sample from each supplier  was also performed to verify that the microstructure was correct.

One company’s samples were good.  The samples from the other company had strength slightly less than the requirement and a microstructure that was sub-optimum.  It was determined that the second company did not have the proper quality processes in place to ensure that shafts would have consistently met the strength requirement.  So, the company whose components did meet the strength requirement was selected as the product supplier of the shafts.

Later, when tooling for making the shaft was ready, samples were made and evaluated composition, strength, and microstructure.  Based on the results, some minor modifications were made to the extrusion process to get the desired microstucture and strength.

Conclusions
Performing the prototype and supplier evaluations discussed here revealed issues early in the product development cycle.  This enabled decisions that were easily implemented, and ensured that the development project stayed on schedule.

Sheet Metal Formability

Formability refers to the ability of sheet metal to be formed into a desired shape without necking or cracking. Necking is localized thinning of the metal that is greater than the thinning of the surrounding metal. Necking precedes cracking.

From the metallurgical perspective, the formability of a particular metal depends on the metal’s elongation, which is the total amount of strain measured during tensile testing. A metal with a large elongation has good formability because the metal is able to undergo a large amount of strain (work) hardening.

Strain hardening
Strain hardening results in an increase of the load-carrying capacity of a metal as it deforms. It also prevents strains from being localized during forming, so the deformation is uniformly distributed throughout a particular section of the material that is exposed to a specific set of forming stresses. As a result, each localized region of the metal thins uniformly during the forming process.

The load carrying capacity of the metal as it deforms is opposed by the reduction in cross-sectional area of the metal as it thins. There is a maximum load where the increase in stress due to the decrease in the metal cross-sectional area becomes greater than the increase in the load-carrying ability of the metal due to strain hardening. Necking begins at this point as the metal starts to thin more in a localized region. Any additional deformation is concentrated in the necking area, while the loads in the surrounding areas decrease.

Strength vs. ductility and elongation
Anything done to increase a metal’s yield and tensile strength does so at the expense of ductility, and therefore elongation. As the elongation of a particular alloy decreases, there is a decrease in the amount of deformation before necking occurs. Strengthening treatments include cold rolling working, through hardening and age hardening heat treatments, and solid solution strengthening. Also, strength increases and elongation decreases as grain size decreases.

Crack formation
Once necking begins, the loads on a metal are concentrated in the necked region.  The amount of deformation of the necked area before a crack forms depends on the microstructure of the metal and the state of stress on the metal.

Cracks that form during metal forming occur by a fracture process that involves the formation and growth of voids around second-phase particles and inclusions in the metal. This is shown in figure below. The voids form, grow, and coalesce to form a crack. So, the presence of second-phase particles and inclusions reduces a metal’s formability because they are sites where cracks nucleate.

VoidFormation

Second-phase particles are often present as a result of adding certain alloying elements or strengthening heat treatments. This is the case for iron carbide particles in steel or precipitates in age hardened alloys.  Inclusions are particles comprised of impurity elements in an alloy. For example, in most steels sulfur is present as an impurity that usually appears as manganese sulfide inclusions. In aluminum alloys iron and silicon present as impurities react with the other elements in the alloys to form hard particles. For an alloy that contains inclusions, reducing the impurity content will help reduce the number of inclusions, and improve formability.

Stress state and formability
Finally, the formability of a metal also depends on the state of stress on a metal during forming. The state of stress depends on the shape of the component being fabricated and the process used to form the component. Forming limit diagrams are used to predict whether the forming strains to which a metal will be exposed will result in necking or cracking.

Why Control Heat Treatment Temperature?

Whether you are through hardening steel, annealing a cold-worked metal, or solution treating an aluminum alloy, the heat treating temperature is critical for obtaining the desired microstructure, and therefore, the desired metal properties.  Microstructure refers to such things as the metallurgical phases present in a metal and the grain size.

Using a temperature that is too hot can result in a metallurgical transformation that proceeds too quickly or the formation of undesired phases.  Using a temperature that is too low can result in incomplete metallurgical transformations, cold worked metals that do not soften sufficiently, or insufficient stress relief.

For example, during the through hardening heat treatment of a carbon steel, the steel is heated to transform all the ferrite and cementite to austenite and then quenched to form martensite.  If the steel is not heated to a high enough temperature, then there is the risk that all the ferrite and cementite does not transform to austenite.  If this occurs, then when the steel is quenched, the remaining ferrite and cementite will be present along with the martensite.  These ferrite and pearlite remnants can weaken the steel.

Another example is cold-rolled sheet metal that is annealed to improve its ductility, and reduce its strength and hardness.  If the annealing temperature is too high, then excessive grain growth will occur.  This will result in the metal having lower strength and hardness than intended.  Also, if the metal is to be formed, there is the risk of orange peel, a cosmetic defect in heavily formed metals with grains that are too large.

So, why might a heat treater use a heat treating temperature that is too high or too low?  To save money, to save time, or just sloppy.  To reduce energy costs a heat treater might try to run its furnaces at the low end of the required temperature range.  However, normal temperature variations throughout a load and normal composition variations within the metal can result in the temperature being too low to cause the desired metallurgical transformations.

To save time, a heat treater might operate a furnace at the high end of the specified temperature range to try to move the metallurgical transformations along as fast as possible.  Again, with normal temperature and composition variations, the temperature may end up being too high, resulting in excessive or undesired changes in the metal’s microstructure.

As for a sloppy heat treater, who knows what you will get from batch to batch of metal stock or components.

To learn more about the effects of temperature control on steel microstructure and properties, take our Metallurgy of Steel Heat Treating course or read Practical Heat Treating by J.L. Dorsett and H.E. Boyer or Steels: Processing, Structure,and Performance  by George Krauss.  Also, the two courses mentioned in the introduction above will discuss the effects of temperature control on precipitation strengthening and annealing cold-worked metals.

Manipulating Metal Properties

When designing products engineers select metals that have specific properties.  What many engineers don’t realize is that when they select a metal with certain properties that they are selecting a composition and a microstructure.  This is because the properties of any metal, and in fact any material, depend on two fundamental factors: composition and microstructure. Manufacturing defects such as voids, inclusions, and seams can also affect the properties of a metal.  However, since we usually try to prevent or minimize defects, their effects will be ignored, at least for this discussion.

For metals, composition refers to the elements present in a metal and their relative amounts.  For example, a 1060 carbon steel contains iron, 0.55 to 0.65% carbon, and 0.60 to 0.90% manganese.

Microstructure refers to the grains and metallurgical phases within a metal and the shape, size, relative amounts, and locations of the phases.  A metal’s microstructure can be observed with a microscope after proper preparation of the metal sample.  Many microstructures can be observed with an optical microscope at magnifications between 25x and 1500x.  Observing microstructure features smaller than about 0.001 mm requires the use of an electron microscope.  The microstructure for the Cu-30% Zn brass shown below consists of grains of alpha brass.  The microstructure for the Sn-37% Pb solder shown below consists of lead particles (dark) in a tin matrix (light).

ColdRolledandAnnealedBrass

Cu-30Zn brass

solder

Sn-37Pb solder

A metal’s microstructure depends on two factors: its composition and the thermal and mechanical conditions to which it was exposed during manufacturing  (the effects of thermal and mechanical conditions during product use will be ignored, which is acceptable for some applications and not for others).  For any particular composition different microstructures can be formed within a metal depending on the manufacturing process and process parameters used to form the metal.  For example, consider a 1060 steel that has been heat treated two different ways.  The microstructure for the sample shown below consists of pearlite and some ferrite.  The microstructure for the other sample consists of spheroidized cementite in a ferrite matrix.  The differences in the microstructures resulted in different strengths and hardness for the two metals.  The sample with pearlite was stronger and harder than the other sample because pearlite is stronger and harder than spheroidize cementite.

Ferrite (white) and cementite (dark) in steel.

1060 steel: Pearlite and ferrite

Spheroidized cementite_compressed

1060 steel: Spheroidized cementite. Reprinted with permission of ASM International. All rights reserved.

Understanding the relationship between properties, composition, microstructure, and processing is critical to 1) selecting a material and the manufacturing processes for fabricating a component and 2) controlling the properties of the material.  These properties include those that are important for ease of manufacturing and those that are important for the performance and reliability of the component being fabricated.  By selecting and controlling the metal composition and microstructure for the components used in a product it is possible to make products that meet their performance, reliability, and cost requirements.

It is important for engineers to recognize that metals, or any other type of material, are not a slab of stuff, but instead consist of various microscopic structures that can be manipulated to obtain specific properties.  Engineers that are good at selecting and controlling these microscopic structures increase their chances of making successful products.

More information about the effects of microstructure on properties and the effects of processing on microstructure is in our Principles of Metallurgy, Metallurgy of Steel Heating, and Corrosion of Metals courses. There are also many books that discuss the relationship between processing, microstructure, and properties.

Engineering Materials for Cost Reduction

One approach to cost reduction is to re-engineer products to use less expensive materials or reduced quantities of higher priced materials.  This approach can have a significant impact on a product’s costs, since the materials used in a product account for a large part of its total cost.

With appropriate risk assessment and design verification, it is possible to make the desired product changes and preserve the required performance and reliability.  In fact, sometimes a product’s performance and reliability is also improved, providing an additional competitive advantage.

The materials engineering approach discussed here is applicable to all types of products, all types of materials (metals, plastics, ceramics, composites, coatings, and adhesives) both common and uncommon materials, and components and materials used to make joints between components.  The trick is to identify the products, components, and materials that offer the greatest opportunity for cost reduction in the shortest period of time.

The balance of this paper provides ideas and examples for re-engineering the materials used in products.

Opportunities for cost reduction

The following situations offer opportunities for cost reduction through materials re-engineering:

  • Products that are over designed.
  • Different product lines with similar components made of different materials.
  • When manufacturing yields are low or the costs of manufacturing are high.
  • Products made using materials selected a long time ago and no one remembers the rationale for their selection.  Or the materials have never been revisited to see if they can be better optimized.

Each of these situations is discussed below.

Over-Designed Products

In some instances, products may be over-engineered using materials that provide way more performance and reliability than necessary.  Such over-engineering can add significantly to the bill of materials cost and to direct labor cost.

Consider the case where steel alloy 4142 was specified, but a 1045 steel would have sufficed.  The 4142 steel was selected when the material was not too expensive, and the design team could afford to use a material that provided way more reliability than needed for the product.  How about the situation where gold plating is used, but tin plating would be sufficient for the desired performance and reliability.  Or the component made of polycarbonate, but could have been made of hi impact polystyrene.

In some designs, the material used in a component is the correct choice but the physical dimensions of the component are overkill, resulting in the use of more of the material than is necessary to meet the performance and reliability targets.

Product over-design is a fairly typical situation in older products that were designed when there was less customer price pressure and manufacturers could afford to have more cost in their products.  It also occurs in new products when design engineers use the same materials repeatedly, without considering other options of materials that might be suitable.

In all of these cases re-engineering can be a fairly straight-forward process that starts with a review of the product performance and reliability requirements and identifying the options of materials that can be used.

Consolidation of Materials

Another opportunity for realizing significant cost reduction is the economy of scale realized through the consolidation of materials used across product lines.  Do your different products use common components made from different materials?  If so, this may offer an opportunity to use the same materials in the different components.  This enables cost-reduction through volume discounts, and the need to carry less inventory of a particular material or type of component.  In some cases, consolidating materials also leads to improvements in manufacturing yields by selecting the materials that are easiest to work with.

For example, a company was using three different grades of polycarbonate for similar types of components.  The company changed to a single grade of polycarbonate for all components and got a price reduction of 10% per pound of plastic resin.  Furthermore, of the three resins, the one that was selected was the easiest to use during injection molding process.  Its use led to a 7% increase in manufacturing yields.

Or consider a large manufacture that used three different solder pastes to build electronics assemblies.  Changing to a single, newer solder paste resulted in 25% reduction in material cost and improvements in manufacturing quality.

Reducing Manufacturing Costs

Manufacturing costs can be reduced by using materials that enable higher yields or higher throughput.  Poor yields are often due to using materials that were selected with only performance and reliability in mind, and not optimized for manufacturability.  Or, the materials may be inherently suitable, but there is too much variation in their properties because the supplier has poor process control.  In either case, inadequate materials make it difficult to make components and form joints that consistently meet their design requirements.  In some cases, this shows up as poor yields.  In others, production line throughput is reduced because the process requires extra attention.

Revisiting Existing Designs

It is beneficial to hold periodic design reviews to determine if there are opportunities to revisit previous materials selection decisions.  This approach is applicable to both long-standing products and designs that are still under consideration.

The design review approach provides an opportunity to consider taking advantage of materials that were not initially available when the product design was contemplated.  It also allows the manufacturing team to take advantage of new, improved methods for processing and joining materials.

The goal of the design review is to look for significant opportunities to reduce bill of material costs, reduce labor content, reduce overall process time, and reduce yield loss.  Addressing any of these issues involves the methods already discussed, namely –

  • Using lower cost materials
  • Redesigning components.
  • Consolidating materials.
  • Using materials that enable increased manufacturing yields and throughput.

As mentioned earlier, re-engineering is a straightforward process that starts with a review of the product design requirements and identifying the options of materials that can be used.

Why Isn’t Everyone Doing This?

There are a few reasons why companies do not look to re-engineering of materials in their products for cost reduction.  First, engineers often do not see materials as an aspect of the design for optimization.  Typically, they first look to modify the mechanical or electrical aspects of a product.

Second, engineers often believe that changing materials will turn into a big research project that will take a long time to complete.  However, this is typically not the case if the proper considerations are made when evaluating and implementing the materials.

The final reason is that engineers may not know of all the options of materials to consider, especially when trying to optimize all of the performance, reliability, cost, and manufacturability requirements.

Many Opportunities

There are ample opportunities in most product designs to achieve significant cost reduction if one knows where to look and what questions to ask.   These techniques are applicable to simple and complex products and to common and high-tech materials.  In many cases it is possible to find materials that not only reduce costs, but also improve product performance and reliability.

The Benefits of Materials Engineering

Published in Stamping Journal October 2005

U.S. stampers are missing an opportunity to gain a competitive edge by offering materials engineering support, which often is lacking within OEMs and Tier 1 suppliers. Many stampers take the position that they “just build to a print”—but so do overseas shops.

OEMs and Tier 1 manufacturers are moving business to global low-cost suppliers. As a result, U.S. stampers try to remain competitive by cutting costs or offering more services.  U.S. stampers are missing an opportunity to gain a competitive edge by offering materials engineering support that the OEMs and Tier 1 suppliers often lack. Instead, many stampers take the position that they just build to a print—but so do overseas shops. So how will U.S. stampers differentiate themselves?

Click here to read the rest of the article

When a Low-cost Supplier Becomes Expensive

This article outlines an eight-step process to help you identify and repair the root cause of a problem that arises when working with suppliers.

I have consulted with manufacturers in many industries. Regardless of the products being produced, they all face the same general challenges and frustrations about product development and manufacturing.  Each of them is concerned about the following questions that impact their profitability:

1.    How can we reduce the time it takes to develop new product?
2.    How can we reduce the costs to make our products?
3.    How can we improve product quality?

With this in mind, let’s look at the following all-too-common scenario with a new, low-cost supplier:

A manufacturer decides to have a component of his product manufactured by a new lower-cost supplier.  The manufacturer receives prototypes from the new supplier and proceeds to build the product using the prototypes.  He performs some tests on the product and decides to change to the new, lower-cost component.  Unfortunately, quality problems start to appear along the way.  For example

  • It is difficult to weld, braze, solder, or glue the component to other components in the product.
  • The component is too brittle and easily breaks during customer use.
  • There are excessive cosmetic defects.

The ripple effects of these problems are:

  1. The product launch is delayed.
  2. The production line is shut down or limps along while the quality assurance staff sorts through batches of components looking for acceptable samples.

For both situations, the manufacturer’s engineers must drop their other projects and fix the new problem quickly, before it becomes too costly.  Meetings, analyses, tests and overtime follow in rapid succession while other projects are delayed.

What follows is a discussion of the steps to take to identify the root cause of the problem and fix it.  The strategy is based upon the understanding that the shape, dimensions, properties, and performance of a component depends on its materials and the response of the materials to the component fabrication processes.  The same concepts can be applied to a sub-assembly and the formation of the joints (welded, soldered, brazed, adhesive) between the sub-assembly’s components.

Fixing the Problem

A component will not perform as required or will have poor reliability due to one or both of the following reasons:

•    The component’s shape, dimensions, or cosmetic appearance do not meet specifications.
•    The component’s materials do not meet specifications for the composition, microscopic structure, properties, or type and number of defects that are present.

In some cases, problems with shape, dimensions, or cosmetic appearance are related to a problem with the materials.

Identifying the root cause of a quality problem requires analysis of the component and its materials in order to obtain the information needed to quickly focus on the potential root causes of the problem.  Without this information engineering teams end up guessing at the possible causes, and their effort is usually not productive.

The following eight-step approach should be used to determine the root cause of the problem so that it can be quickly corrected:

1.  Gather all known requirements for the component. These include the component’s shape and dimensions, its materials, performance requirements, and reliability requirements.  Reliability requirements refer to the use conditions to which the component will be exposed during its use and the allowable performance degradation after exposure to the use conditions.

2.  Get samples of the component for analysis of the component and its materials. Samples of both good and bad samples should be obtained. The analysis data from the good samples will be used as a benchmark against which the data from the bad samples can be compared.  In addition to analyzing the bad samples, it is also helpful to evaluate good samples to verify that the materials do indeed satisfy their requirements.  Sometimes, something works even though it doesn’t meet its specifications.  This can make problem solving very difficult if it is not known what the supplier was doing right in the first place.

3.  Gather information about the manufacturing processes that were used to make the component. Find out the process steps and process conditions.  This information is important to help understand the results of the analyses discussed in the next step.

4.  Identify the analyses that need to be performed. Analysis of the shape, dimensions, and cosmetic appearance is fairly straightforward.  Analysis of the materials that comprise the component can include analysis of a) composition, b) microscopic structures, c) properties, and d) defects in the material.  The specific analyses to perform depend on the component’s design requirements and the types of materials that make up the component.  Work with the lab analyst to get her input about the analyses that should be performed.  This will require providing as much information about the problem as possible to the analyst.

5.  Perform the analyses.

6.  Review the analysis results and identify possible root causes of the problem. The root cause can be related to the materials used to make the component, an error by the operator on the component production line, the manufacturing equipment, or the manufacturing steps or process parameters used to fabricate the component.  The data from the analysis should help focus on a few potential root causes.  Sometimes, the root cause is obvious.  In other cases, some work is required to verify a specific root cause for a particular problem.

7.  Provide feedback to the supplier. The supplier may need help figuring out what to do to control or change the manufacturing processes in order to produce a component that meets all of its requirements.  The materials analysis information will help the supplier understand what is required.  After the supplier has made the necessary changes get new samples of the component and have them analyzed to verify that the problem was fixed.

8.  Update the component’s specifications. A potential root cause is that the specifications for the component did not have enough detail, resulting in a component that met the specifications, but did not work as required.  If this was the case, then the specifications must be updated to include the missing shape, dimensional, cosmetic, and/or materials requirements.

Product Design, Manufacturing, and Materials

Designing and manufacturing a mechanical, electrical, or electromechanical device requires thorough specification of the materials properties of the individual components and controlling the materials properties. Doing these will help ensure high manufacturing yields, good quality, and good reliability.

For some products the materials requirements are minimal, allowing for a wide range of material variation in order to produce the final product. Other products with many materials requirements (e.g. automotive, medical, appliances) require tight control of the materials properties.

There are many opportunities during the course of designing a product to get information about the materials properties, how tightly they must be controlled, and the ability of suppliers to maintain the required control. These include:

  • Perform a literature review to determine if the materials have been used in a similar application, how the materials are expected to degrade, and the expected reliability of the materials.
  • For materials such as adhesives, solder paste, coatings, etc. recognize that supplier materials properties data is probably nominal. However, all materials’ properties have some degree of variation. Have the materials properties analyzed (use at least 3 separate production lots) to determine the expected variations. Use this information to help write the materials specifications. Also, use the same 3 lots of material for process development. Keep data on the development yields vs. materials properties.
  • For custom made components (e.g. castings, moldings, stampings) get samples of similar parts that were made by the supplier. Have some of the basic materials properties of the parts analyzed to determine the supplier’s ablility to make the components to the required specs and to get an idea of the expected variation. A little bit of money spent on this at the beginning of a program can have a huge payback, especially if it is determined early in the program that the supplier is not capable.
  • Characterize materials interactions by performing accelerated life tests on a sub-set of components. This should be done in parallel with the other design efforts. The information will enable the design team to assess the expected reliability without having to build the entire product, giving the team a chance to test more than one material at a time. It will also provide data for specific materials and components that can be used in future supplier, quality, performance, and cost reduction efforts.
  • Evaluate the materials properties before and after product validation testing to have a correlation between materials properties, degradation, and performance. This information may also be useful at a later date if there are problems with supplier or product quality.
  • Review the design with a materials engineer to detemine if better materials options exist.
  • Write thorough materials specifications for all the components and materials used in the product.

All these items can be done in parallel with the typical mechanical design effort. The companies that are successful at taking avdantage of these opportunites will find it easier to meet project deadlines and encounter fewer surprises. The others will have opportunities to work on failure analyses, spend time on daily conference calls with frustrated customers, and figure out if they supplier or internal manufacturing problems.

Selecting Capable Suppliers – Part 1

Michael Pfeifer, President, Industrial Metallurgists, LLC
Herb Shields, President, HCS Consulting

Suppliers of components and sub-assemblies are critical to the success of most companies.  Companies depend on their suppliers to provide an item that always satisfies its design requirements and is always delivered on time.  However, companies do not always use a methodical approach for evaluating and selecting suppliers.  Instead, they are lured by the promise of a low piece part price, only to find that the costs due to poor quality and delayed product launch quickly overshadow the planned savings.  This article explains how to select suppliers that will enable production at the lowest total cost and highest quality.

Consider the company that used a low-cost supplier to fabricate a plastic sub-assembly for a brand new product.  The sub-assembly, which consisted of two plastic components that were joined by ultrasonic welding, was a critical part of the product.  Soon after the product was launched failed samples started coming back from customers.  The weld joint was failing because the welds were poorly formed.  To make matters worse, the supplier was not capable of fixing the problems with its manufacturing processes, so the problem dragged on and overwhelmed the original excitement with the new product.  Ultimately, the problems with the weld joint caused the product to be unsuccessful.

Maximizing the likelihood of selecting optimum suppliers requires that design and purchasing teams have the resources, expertise, and discipline to do the following:

    1. Evaluate the technical importance of the components and sub-assemblies used within the product.
    2. Set supplier selection criteria.
    3. Evaluate suppliers to determine if they meet the selection criteria.

This article discusses the considerations required for improving the likelihood of properly performing these three tasks.  These considerations are based on the materials engineering and supply chain perspectives.

Materials Engineering Perspective

The materials engineering perspective is based upon the following three considerations:

    1. The performance, reliability, and cost of a product are strongly dependent on the properties of the materials that comprise the product.
    2. Proper selection of the materials that make up a product is crucial in order to satisfy the desired performance, reliability, and cost requirements of the product.
    3. Control of the variation of the properties of the materials that make up a product is crucial for enabling the consistent performance, reliability, and cost of the product.

With respect to supplier selection, the first and third considerations are significant.  Both considerations help design and sourcing teams focus on selecting suppliers that have the expertise and capabilities to provide a component or sub-assembly whose materials enable the component or sub-assembly to satisfy its design requirements.

Suppliers must be capable of developing manufacturing processes that result in the proper properties for the materials that make up their products.  This means that suppliers must understand the materials and manufacturing processes being used in order to ensure that their products meet the performance and reliability requirements specified by their clients.  This applies to the materials the make up individual components, components within a sub-assembly, and joints between components in a sub-assembly.

A supplier must be able to control the variation of the materials used to make its product and the variation of its manufacturing processes so that the materials in the process output have consistent properties from sample to sample.  If the properties of the materials in the process output vary too much from sample to sample, then the performance and reliability will be inconsistent from sample to sample.  Furthermore, inconsistent materials properties can hurt the manufacturability of the product made using the component or sub-assembly.

Supply Chain Perspective

The supply chain perspective is based upon the following three considerations:

    1. Suppliers must be selected based on their ability to provide components and sub-assemblies that minimize the total cost to build a product.
    2. Suppliers must be selected based on their ability to maximize assurance of production supply.
    3. Suppliers must be selected based on their ability to provide components and sub-assemblies that consistently meet their design requirements.

Total cost includes all costs, not just the purchase price.  Transportation, inventory, quality, import duties, etc. all need to be included in the cost analysis.  The best supplier should have the ideal balance between all three factors.  This may or may not be the supplier with the lowest piece price.  Focusing on only the unit price of the item being supplied will possibly result in increased costs due to poor quality or service.  Purchasing and design teams should focus on reducing the overall risk to product success.

Assurance of production supply relates to delivering quality products on time and in the correct quantities.  Also, there must be some assurance from the prospective supplier that they have sufficient capacity to meet your requirements if demand grows.  This commitment probably cannot be open ended, but suppliers should have some contingency plans in place.

In today’s global economy, high quality must be a given with any prospective supplier, otherwise there is no reason that they should be considered.  A supplier must be able to control its process within specified parameters in order to produce an item that consistently meets its design requirements.

Assessing the Technical Importance of Components and Sub-Assemblies

Technical importance refers to the impact of a particular component or sub-assembly on the performance and reliability of a product.  Within any product the components and sub-assemblies cover a spectrum from low importance to high importance.  A high importance item has significant contribution to the performance and reliability of one or more of a product’s
functions.  A low importance item has little contribution to the performance and reliability of any of a product’s functions.

For example, consider a lightweight, high performance bicycle.  Examples of high importance items are the frame sub-assembly and the sub-assemblies within the gear shift sub-assembly.  Examples of low importance items are the seat and reflectors.  This is not to say that the seat and reflectors are not necessary parts of a bicycle.  However, they do not influence the bicycle’s performance in a way that provides substantial differentiation compared to other bicycles.

Identify Supplier Selection Criteria

Selection of a capable supplier involves consideration of many different criteria that can be placed in the following categories:

    1. Technical expertise and capabilities.
    2. Manufacturing capabilities
    3. Manufacturing capacity.
    4. Manufacturing competence.
    5. Ability to provide technical assistance.
    6. Supply chain organization.
    7. Production planning process.
    8. Shipping and logistics.
    9. Geographic location.
    10. Company size and financial stability.
    11. Delivered cost.

Each category and the supplier evaluation process will be discussed in next month’s newsletter.

Selecting Capable Suppliers – Part 2

Michael Pfeifer, President, Industrial Metallurgists, LLC
Herb Shields, President, HCS Consulting
Suppliers of components and sub-assemblies are critical to the success of a product.  This is the second part of a two-part article that discusses the considerations for selecting suppliers that will enable production at the lowest total cost and highest quality.  The first article discussed the materials engineering and supply chain perspectives that must be considered when evaluating and selecting suppliers, and ended with a list of supplier selection criteria.  This article explains the considerations for each of the selection criteria and discusses the evaluation process.

 

Identify Supplier Selection Criteria

Selection of a supplier involves consideration of the following different categories of criteria:

    1. Technical expertise and capabilities.
    2. Manufacturing capabilities
    3. Manufacturing capacity.
    4. Manufacturing competence.
    5. Ability to provide technical assistance.
    6. Supply chain organization.
    7. Production planning process.
    8. Shipping and logistics.
    9. Geographic location.
    10. Company size and financial stability.
    11. Delivered cost.

Each of these categories is discussed next.

Technical expertise and capabilities. Is the supplier knowledgeable about the materials to be used in the sub-assembly or component?  Does the supplier have experience with the materials and processes required to make the item under consideration?  Does the supplier have the technical expertise to work out manufacturing problems?

From the materials engineering perspective, design teams should be concerned with a supplier’s experience with the materials used in the item being provided and with the manufacturing processes used to manipulate the materials into the item to be made.   A supplier must also have the technical knowledge required to identify, assess, and mitigate risks to meeting the development schedule.

Manufacturing capabilities. This refers to the different manufacturing processes that are available, and the capabilities of the manufacturing equipment.  Things such as the capability of fabricating very large or very small components, or the capability to perform different primary and secondary processes are a few of the considerations when assessing manufacturing capabilities.

Manufacturing capacity. This refers to the number of components or sub-assemblies that can be produced in a period of time.  From the supply chain perspective, how much capacity is available for this product and is there an alternate plant or equipment that could be utilized if needed?  Is the supplier prepared to commit the necessary capacity on a long term basis?

Manufacturing competence. Is a supplier capable of controlling its manufacturing processes in order to produce a component or sub-assembly that consistently meets its design requirements?  Does the supplier have manufacturing experience that is directly applicable to the item under consideration?
It is important to understand the process variation, and compare it to the specifications for the item to be made.  If the supplier’s standard deviation is more than what is required for your component or sub-assembly to work, then this must be discussed before going into production.  Even if there appears to be no issue, it is important to understand how the process is controlled on an ongoing basis.

Ability to provide technical assistance. A design team may determine that it does not have all of the expertise to make certain decisions about the design of its product, and may want outside expertise.  Many suppliers have a great deal of technical expertise.  In fact, an experienced supplier will have in-depth knowledge in their area of expertise combined with experience working on a wide range of different products for different customers.  Suppliers like this have the knowledge and perspective that enable them to offer design suggestions about the options of materials and manufacturing processes that can be considered.

Geographic location. Is it important for the supplier to be located nearby for ease of communication, ease to visit, and speed of delivery?  Or is it acceptable for the supplier to be on the other side of the world.  From the materials perspective this decision will affect the ability to assist with the supplier’s product and process development and to assist with product quality problems that arise during production.  This is an important consideration from the supply chain perspective.  Off shore suppliers will mean longer lead times for shipments of components or sub-assemblies.  Inventory costs and transportation costs will be higher with a global supply chain.

Supply chain organization. The supply chain extends beyond the supplier to its suppliers as well.  It is important to understand what commodities are used by your supplier, who the key sources are, and what type of relationship exists between your supplier and its sources.

Production planning process. Is the supplier able to schedule production in lot sizes and frequency that match well with your projected requirements?  If you are going to produce your product in 1000 piece lots every week, then does the supplier have sufficient available capacity and can its supply chain support weekly production of raw materials and components?  What is the lead time that the supplier needs to produce products on a regular basis?  Does the lead time exceed the forecast or ordering information that is available from customers?

Shipping and logistics. You should agree on frequency and lead times associated with shipments of product from your suppliers.  Does the supplier have a back up plan if weather or other issues affect the primary mode of transportation?

Company size and financial stability. All other things being equal, the size of a company and its financial stability are indicators of the resources that can be brought to bear to solve problems.  Also, for long term projects the financial stability is an indicator of the likelihood that a company will be able to meet its obligations to its customers over the entire length of the project.  If this is likely to be a long term relationship, meeting with the supplier’s management team is an important step.  Establishing a good relationship from the start will make problem resolution easier to handle going forward.

Delivered cost. Delivered cost includes all costs, not just the purchase price.  Transportation, inventory, quality, import duties, etc. all need to be included in the cost analysis.  The best supplier may or may not be the supplier with the lowest piece price.

Supplier Evaluation

Evaluation of suppliers involves an audit of suppliers to assess their ability to satisfy the critical items from the list above.  The assessment should include a questionnaire and evaluation of the suppliers’ product and be conducted by a cross functional team that includes representatives from purchasing, quality, engineering or R&D, manufacturing, and scheduling.  With a rating scheme developed by the team it is possible to objectively rate suppliers based on all the information.

A questionnaire is useful for obtaining basic information about the general capabilities of a supplier and its systems for ensuring that its product is delivered on time and with the desired quality.  The team should visit and administer the questionnaire to potential suppliers of high importance items.  For lower importance and overseas suppliers it may not be practical to send the entire team, which is acceptable provided that the audit team has a well documented process for obtaining the desired information.  The team can meet with the people who conduct the audit and make a decision.

Evaluation of a prospective supplier’s product is important for verifying its ability to provide an item that consistently meets its design requirements (i.e., performance and reliability).   This is information that cannot be obtained through a questionnaire.  From the materials engineering perspective the evaluation involves analysis of the materials in the suppliers’ products, which will help determine if a supplier is capable of controlling the materials and manufacturing processes used to make its product.  The analyses to perform include those for the materials’ composition, various microscopic features, significant properties, and defects.  This approach makes sense since the performance and reliability of any item is directly related to the properties of the materials that make up the item.  The properties depend on the materials’ composition, various microscopic features, and defects.

For a custom-made item the analyses can be performed on a similar item that the prospective supplier already produces.  For and off-the-shelf item the analyses can be on samples of the actual item.  The audit team must identify the significant materials that should be analyzed and the significant materials properties, composition, microscopic features, and defects to evaluate.  Any problems uncovered by the analysis will likely be present in the component or subassembly to be made for the design team.

As an example, consider a sub-assembly consisting of welded metal components.  The evaluation team should have the weld joint analyzed for its strength, microstructure, presence of defects like voids and cracks, and weld shape.  Samples can be taken from an item that is already in production at the supplier’s factory.

Money, time, and effort must be spent to properly evaluate suppliers. However, it is a relatively inexpensive way to mitigate the risks of selecting a supplier that is not capable of properly designing and manufacturing the component or subassembly. Furthermore, the analysis is much less expensive than missed deadlines or low process yields related to poor supplier quality.

Finally, the complete audit may indicate that a supplier has strengths in areas that offer a significant competitive advantage, but is weak in other areas.  For example, a supplier may have special manufacturing capabilities or technical competence; however, the variation of the manufacturing processes is excessive.  In this case, the design team can work with the supplier to help it reduce the variations.

Product Success

The methodologies and considerations discussed in this article are critical for improving the likelihood of selecting suppliers that can contribute to the success of your product.  None of what is discussed here is new.  It just requires focus and discipline.  However, there are many companies that struggle with problems that are a direct result of using incapable suppliers because their supplier selection processes are inadequate.

Precipitation Strengthening

The strength of metals is improved by impeding the motion of dislocations through the metals. One approach to achieving this improvement is to form a uniform distribution of closely spaced sub-micron sized particles throughout an alloy. The particles, which are called precipitates, impede dislocation motion through the alloy. Not every alloy can be precipitation strengthened. Alloys that can be precipitation strengthened include Al-Cu, Al-Mg-Si, Cu-Be, and 17-8 PH steel. The figure shows precipitates in a Al-Cu alloy.

Al2Cu precipitates in a Al-4% Cu alloy. © DoITPoMS Micrograph Library, Univ. of Cambridge

Al2Cu precipitates in a Al-4% Cu alloy. © DoITPoMS Micrograph Library, Univ. of Cambridge

The particles are formed by precipitation, which involves a series of heat treatment steps. The first step is solution heat treatment. This involves heating the alloy up to a temperature that results in the atoms of the alloying element being dissolved within the solid structure formed by the array of atoms of the main element. For Al-Cu alloys, the copper atoms dissolve into the array of aluminum atoms. The dissolved structure is then retained at ambient temperatures by cooling the alloy rapidly, such as by water quenching.

After cooling, precipitates are formed either by natural aging or artificial aging.  With natural aging, the precipitates form at room temperature. With artificial aging, the precipitates form when an alloy is heated to a temperature lower than the solution heat treatment temperature. Only certain alloys will undergo natural aging. The other alloys must be artificially aged.

Regardless of the aging process, as the precipitation process proceeds the precipitates go through a series of stages, with changes in the size, form, and composition of the precipitates. The particular stage of the precipitates has a direct influence on the strength of the alloy. For artificially aged alloys, this is controlled by the aging temperature and time. At any particular aging temperature, there is an aging time at which the alloy will reach its maximum strength. This maximum strength corresponds to a specific stage of the form and composition of the precipitates. Aging for a time that is too short or too long will result in less than maximum alloy strength.

For artificially aged alloys, the aging temperature affects the maximum strength that can be obtained, and the time required to reach maximum strength. For naturally aged alloys, the strength increases over time. The time required to reach maximum strength depends on the alloy.

Finally, precipitation strengthening can be combined with cold-working to give even greater alloy strength.

More information about the metallurgy of precipitation strengthening and precipitation strengthening heat treatment is in our Precipitation Strengthening course. Also, Heat Treatment: Structure and Properties of Nonferrous Alloys by C. R. Brooks, Precipitation Hardening by J.W. Martin, and ASM Handbook, Volume 4: Heat Treating discusses precipitation strengthening.