Factors Influencing Design (1): Manufacturing Considerations
Why Manufacturing Considerations Shape Design
A design that cannot be manufactured efficiently, or that costs far more to produce than the market will pay, is not a viable engineering solution. Manufacturing considerations are the practical and economic realities of making the product, and they must be built into the design from the earliest stages. You need to understand how scale of manufacture, material availability and form, types of manufacturing processes, and production costs all influence design decisions.
Scale of Manufacture
The number of units a product will be made in — its scale of manufacture — fundamentally changes which processes, materials and designs are cost-effective. There are three main scales.
One-off production means a single unique item is made to a specific brief — a bespoke piece of jewellery, a prototype, or a custom-built racing car component. Tooling is minimal and designs can be highly complex, but unit cost is very high because setup costs are absorbed by a single item. Batch production makes a defined quantity of identical items — a run of 500 specialist brackets or a print run of educational kits — before the machinery is reset to make something different. Unit cost falls compared to one-off because setup costs are spread across many units. Mass production makes very large quantities continuously, often using automated assembly lines — car body panels, plastic bottle caps, electronic circuit boards. Unit costs are very low but this scale requires large capital investment in dedicated tooling and machinery. The design must be optimised for automated manufacture: complex geometry, tight tolerances or hand-finishing are prohibitively expensive at mass scale.
The three scales of manufacture are one-off (single unique item — e.g. a bespoke prosthetic limb), batch (a defined quantity — e.g. 1,000 metal brackets) and mass production (very large, continuous quantities — e.g. plastic bottle caps). The scale chosen affects which processes are viable, what unit cost is achievable, and how much design complexity the manufacturing method can accommodate.
Material Availability and Form
A designer cannot simply choose the theoretically ideal material for a product — they must also consider whether that material is available in the form required for the chosen manufacturing process. Material form refers to the standard shapes and sizes in which materials are commercially supplied: sheet, plate, bar, rod, tube, angle section, I-section, wire and powder, among others. A design that requires a bespoke cross-section will need extrusion or machining from solid stock — both more expensive than using standard sections. Designers minimise waste and cost by aligning part geometry to standard material forms wherever possible.
Material availability also encompasses supply chain reliability, lead times and sustainability. A material that is difficult to source, has long lead times or is subject to price volatility adds risk to the project. If a critical material becomes unavailable mid-production, the entire design may need to be revised. Specifying readily available, standard materials reduces risk and often reduces cost.
There are six categories of manufacturing process and you need to know how the choice of process influences design. Wasting processes remove material from a larger piece — cutting, drilling, milling and turning are all wasting processes. The design must allow tool access to every surface that needs to be cut. Shaping processes use moulds or dies to form material into a shape — injection moulding and die casting are shaping processes. Design for shaping must consider draft angles (slight taper to allow the part to release from the mould) and uniform wall thickness to avoid sink marks and warping. Forming processes deform material without removing it — bending, rolling, pressing and forging. The design must account for spring-back in sheet metal bending and grain direction in forging. Joining processes fix two or more parts together — welding, brazing, soldering, riveting, bonding and mechanical fasteners. The design must include sufficient material thickness and access for tools at the join location. Finishing processes improve the surface of a product — painting, powder coating, anodising, plating and polishing. The design must avoid internal corners and recesses that traps residues or prevent even coating. Assembly is the combination of components into the final product — the design must ensure that parts can be brought together in a logical sequence and that tolerances allow for consistent fit.
Production Costs
Every manufacturing decision has a cost implication. Production costs are divided into two categories. Labour costs are the costs of the human work involved in making the product — direct labour (workers on the production line) and indirect labour (quality inspectors, supervisors). Labour costs are a major design driver: a design that requires extensive hand-finishing or complex assembly by skilled workers will be expensive to manufacture. Automating or simplifying assembly steps reduces labour cost but may require capital investment.
Capital costs are the costs of the machinery, tooling, moulds and equipment needed to manufacture the product. A new injection-mould tool can cost tens of thousands of pounds — this cost is only justified if the production volume is large enough to spread it. At one-off or small-batch scale, designs should use processes with low capital cost (such as laser cutting from standard sheet rather than injection moulding) even if the per-unit process cost is higher. At mass-production scale, high capital investment in tooling is justified because the cost per unit falls dramatically with volume.
Production costs are split into labour costs (human work) and capital costs (machinery and tooling). At high volumes, capital investment in tooling reduces unit labour and process costs significantly. At low volumes, high capital costs cannot be recovered, so designs should use low-tooling processes. Understanding this relationship between scale and cost is a central concept.
Imagine a designer has created an ideal form for a new plastic enclosure for an electronic device. If the product will be mass-produced at 100,000 units per year, injection moulding is viable — the £40,000 mould tool cost is recovered across the run. The designer must now add draft angles to all vertical walls, make wall thickness uniform at around 2 mm, and avoid undercuts that would prevent the part ejecting from the mould. If the same enclosure is needed for a 50-unit batch prototype, injection moulding is completely uneconomical. The designer instead uses laser-cut acrylic sheet and solvent bonding — a different set of material forms, joining processes and finishing treatments. The product's function is identical, but its manufacturing-driven geometry is different in both cases. This illustrates why manufacturing considerations are not an afterthought but a fundamental design input from the start of the process.