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When a product transitions from prototype to mass production, material selection becomes a critical factor. The initial focus on speed and availability gives way to a new set of priorities: repeatability, cycle time, and supply chain stability. At high volumes, even minor per-unit cost reductions yield substantial profit gains, while small inefficiencies are amplified. A material that works for a single prototype might fail under the stresses of continuous manufacturing or cause excessive tooling wear, resulting in costly downtime.
Furthermore, the cost structure shifts. In low-volume production, labor dominates, whereas in high-volume scenarios, raw material costs are the primary driver. Supply chain reliability also becomes paramount, as relying on a single-source specialty material introduces significant risk. For these reasons, making a strategic and informed decision when choosing the right material for high-volume parts is a financial and operational imperative.
Analyzing Total Cost of Production
Product teams often mistake the price per pound of raw material for the total cost. While the raw material price matters, the material's processing characteristics have a greater impact on the final bottom line. A cheaper plastic that requires a longer mold-cooling time increases cycle time. If a machine produces fewer parts per hour, the overhead cost per part rises, negating the savings from the cheaper resin.
Material Waste and Scrap Rates
High-volume processes like machining or stamping generate scrap. When selecting metals, the team must calculate how much material ends up on the shop floor versus in the final part. Stamping processes enable nesting of parts to minimize waste, but the material's grain structure must support this orientation. In injection molding, runners and sprues represent waste unless the facility can regrind and reuse the material. Material selection influences the viability of regrinding, as some polymers degrade significantly after the first heat cycle.
Tooling Implications
Harder, more abrasive materials demand robust tooling. For metal parts, machining stainless steel wears out cutting bits faster than aluminum or brass. In injection molding, corrosive plastics such as PVC require stainless steel molds to prevent rust and pitting, which are more expensive than standard tool steel. The material choice sets the baseline for the tooling capital investment.
Matching Material to Manufacturing Method
The chosen manufacturing method narrows the field of available materials. High-volume production typically relies on injection molding for plastics and die casting, stamping, or automated machining for metals. Each process imposes distinct physical limitations on the material.
Injection Molding Constraints
Thermoplastics dominate high-volume plastic production. The material must melt consistently, flow into intricate mold cavities, and solidify without excessive warping.
- Melt Flow Index (MFI): This metric indicates how easily a polymer flows. Thin-walled parts require a high-MFI material to fill the mold before solidification.
- Shrink Rates: All plastics shrink as they cool. The engineer must predict this shrinkage to hold dimensional tolerances. Crystalline plastics, such as acetal, shrink more than amorphous plastics, such as ABS.
- Gate Vestige: The material must break away cleanly from the mold gate. Some tough materials leave sharp or unsightly marks that require manual trimming, increasing labor costs.
Metal Processing Considerations
For metal components, machinability and formability guide the decision.
- Stamping: The metal needs ductility to form shapes without cracking. However, it also requires enough rigidity to hold its final shape. Spring steel offers this balance but challenges the tooling.
- Die Casting: Zinc and aluminum serve as the standards for high-volume die casting due to their relatively low melting points and fluidity. Steel, with its high melting point, is unsuitable for this process.
- Machining: Free-machining alloys contain trace elements like lead or sulfur to help break chips and lubricate the cutting tool. These additives drastically improve production speed compared to standard alloys.
Evaluating Performance Requirements
The operating environment of the final product defines the "must-have" properties. High-volume parts often end up in consumer goods, automotive applications, or industrial equipment, all of which face different stressors.
Thermal Management
Temperature fluctuations cause materials to expand and contract. If an assembly pairs a plastic housing with a metal chassis, the mismatched thermal expansion rates can induce stress fractures or loosen fasteners. High-temperature environments exclude standard commodity plastics such as polyethylene, prompting engineers to consider engineering resins like PEEK or Ultem, despite their higher cost.
Chemical and UV Resistance
Outdoor products face relentless UV exposure. Without UV stabilizers, many plastics become brittle and discolor within months. Chemical exposure also dictates specific resin choices. A medical device wiped down daily with harsh disinfectants requires a material that resists stress cracking, such as polypropylene or specialty copolyesters.
Mechanical Loads
Understanding the type of load matters. A part under constant tension imposes different demands than a part subjected to sudden impacts. Nylon offers excellent tensile strength but absorbs moisture, which changes its dimensions and stiffness. Polycarbonate provides high impact resistance but cracks easily if exposed to certain solvents.
Supply Chain Security
Availability frequently trumps performance in mass production. A "perfect" material that requires a 20-week lead time disrupts the entire business model. High-volume production consumes raw materials at a ferocious pace.
Avoiding Single Sources
Innovative procurement strategies involve qualifying equivalent materials from different manufacturers. If the primary supplier experiences a shortage, the factory switches to the approved backup without halting production. Commodity grades of ABS, polypropylene, and aluminum are typically widely available, making them safer bets than proprietary blends available from a single distributor.
Consistency Across Batches
In large production runs, material consistency guarantees part quality. Variations in resin viscosity or metal hardness force the machine operators to constantly tweak process parameters, leading to rejected parts. Established material suppliers provide certificates of analysis (COA) with each batch, verifying that the properties fall within the agreed-upon range.
Regulatory and Compliance Factors
Global markets enforce strict regulations on material composition. Failing to comply with these rules creates legal liability and impedes market access.
- RoHS and REACH: These European standards restrict hazardous substances like lead, mercury, and cadmium. Most electronics and consumer goods must comply.
- FDA Compliance: Materials contacting food or used in medical devices must meet specific purity standards. The supplier must provide documentation certifying the material's suitability.
- UL Ratings: Electronics enclosures often require a specific flammability rating (e.g., UL 94 V-0). The material must self-extinguish within a set time if ignited.
Final Validation and Testing
Before committing to a large-scale purchase order, the selection must be validated through rigorous testing. Using prototype molds or soft tooling enables engineers to produce a small batch of parts with the specified production resin. This phase is a critical component of design for manufacturing, as it uncovers issues that 3D printing or computer simulations may overlook, such as knit lines, warping, or surface finish defects.
Testing these pilot parts involves subjecting them to simulated real-world conditions. Drop tests, thermal cycling, and chemical exposure tests confirm the material's durability. By identifying potential failures at this stage, the team can pivot to an alternative material before investing in expensive, hardened production tooling, ensuring the final product is optimized for large-scale manufacturing.
Aligning Engineering with Business Goals
The optimal material represents a trade-off between cost, performance, and availability. Your success ultimately depends on choosing the right material for high-volume parts, ensuring both manufacturability and supply chain resilience.
Developing a product for mass production demands a comprehensive materials and manufacturing strategy. SGW Designworks guides companies through these complex decisions, minimizing risk and accelerating time-to-market. Contact our team to optimize your product for high-volume success.
