SiliciumHex FieldKit

Design to Cost · Generate

Material Substitution

Challenge each material against alternatives on cost, process, quality and risk — with real quotes, not catalogs.

  • Time45 min
  • FormatSolo
  • StageGenerate

Material Substitution: what it is and why it works

Material substitution challenges each significant material in a product against alternatives on cost, processability, quality and risk. The team lists the materials used and their cost share, and for each high-share material identifies candidate substitutes that could be cheaper, lighter or easier to process. Candidates are checked against the product's real requirements, rederived from function and operating conditions rather than inherited from an earlier specification. The most promising are costed with real supplier quotes, prototyped and tested, and validated substitutions are recorded in the design rules.

Material choices are often made once and then carried forward for years, while prices, supply conditions and material technology change. Reexamining them can unlock significant savings, especially when a different material also allows a cheaper process, for example molding instead of casting and machining. The approach draws on value engineering practice and on the materials selection tradition associated with Ashby, which compares materials using performance indices that combine properties with density and cost. Material changes interact with process choice and design, so substitution is often combined with process redesign and DFM/DFA reviews, and should-cost models help compare the full cost of each option.

What you need

  • A list of materials used in the product with their cost share
  • The functional and operating requirements: loads, temperatures, environment, lifetime, regulatory requirements
  • Candidate substitute materials and their properties
  • Supplier quotes for the part in each candidate material, including any tooling
  • Test facilities or partners for prototypes

What you get

  • A shortlist of substitutions with cost, process and risk evaluation
  • Rederived requirements for each part studied
  • Prototype test results for the most promising substitutions
  • Validated substitutions recorded in the design rules, with their limits of use

When to use it

When a material was chosen years ago and prices have moved since.

How to do it, step by step

  1. List the materials used and their cost share.
  2. For each high-share material, list candidate substitutes: cheaper, lighter, easier to process.
  3. Check substitutes against the real requirements, not the spec inherited from the last project.
  4. Prototype the most promising substitutions and test them.
  5. Record the validated substitutions in the design rules.

Worked example: Terminal box cover for industrial motors

Illustrative scenario — figures are realistic but not from a real company.

A motor manufacturer used a die-cast aluminum terminal box cover on its general-purpose industrial motors, about 40,000 units a year. The cover cost $14.80 including casting, machining and paint. The aluminum choice dated back more than 15 years.

  1. Cost analysis showed the cover among the largest material cost items in the terminal box. The team listed candidates: a different aluminum alloy, sheet steel, and glass-fiber-reinforced polyamide (PA66-GF30).
  2. They rederived requirements: enclosure sealing class, impact resistance, operating temperature range, UV exposure outdoors, flammability, and torque retention on gasketed joints. Motors for hazardous locations were excluded, because their enclosures must remain metallic under the applicable certification.
  3. Supplier quotes put the molded PA66-GF30 cover at $6.90 with a $95,000 mold, and the steel option at $11.20.
  4. Prototypes in PA66-GF30 with brass threaded inserts were tested for impact, thermal cycling, UV aging, sealing and torque retention. The first design failed torque retention, and bosses were redesigned before passing.
  5. The validated substitution and its limits, general-purpose motors only, were added to the design rules.

Result. The new cover saved about $7.90 per unit, roughly $316,000 a year, with the mold paying back in about four months. The explosion-proof range kept aluminum. The team noted that the failed first test was the most useful part of the project, because it defined the design rule for plastic bosses.

Open it in the FieldKit Design to Cost app → Get the Design to Cost template pack — join the waitlist

Common pitfalls and how to avoid them

  • Comparing materials on catalog price per pound.Compare full part cost with real quotes, including process, tooling, finishing and scrap.
  • Defending or rejecting a material based on an inherited specification.Rederive requirements from function, operating conditions and regulations before evaluating candidates.
  • Skipping prototype testing because the material data sheet looks sufficient.Test prototypes under realistic conditions, including long-term effects such as creep, aging and corrosion.
  • Applying a validated substitution beyond its tested limits.Record the limits of use in the design rules, for example excluding hazardous-location products.

Frequently asked questions

How do you choose a substitute material?

Start from the part's functional requirements: loads, temperatures, environment, lifetime and regulations. Screen candidate materials against those requirements, then compare full part cost, including the process each material allows. Get real supplier quotes for the leading candidates, build prototypes and test them under realistic conditions before deciding.

What is an Ashby material index?

An Ashby material index combines material properties into a single figure of merit for a given function and constraint. For example, for a light, stiff beam in bending, the index is the square root of Young's modulus divided by density. Dividing by cost per unit mass instead gives a cost-based index. Materials with higher index values perform better for that specific design case.

What are the risks of material substitution?

The main risks are unexpected long-term behavior, such as creep, aging, corrosion or fatigue, differences in processing that affect quality, supply risks for the new material, and regulatory or certification issues. These risks are managed by rederiving requirements, testing prototypes under realistic conditions, qualifying suppliers and defining clear limits of use.

Origin

Material selection for cost — value engineering practice; Ashby material indices tradition.

Used in these playbooks

Sourcing cost-push month 1 month

One month focused on bought-in cost: pareto the spend, substitute materials, settle make-or-buy and lock a cost-down curve with key suppliers.

  1. Cost Pareto
  2. Material Substitution
  3. Make or Buy
  4. Cost-Down Agreement

Related methods

More in “Generate”

Produce reduction ideas from functions, design rules and process rethink.