ABS Injection Molding

Why ABS is the easy one

Injection molding rewards materials that behave predictably, and ABS behaves predictably at every stage of the cycle.

Stage	ABS	What it means
Melting	Wide window, ~210–270 °C	Forgiving of machine and heater variation
Mould temperature	Moderate, ~40–80 °C	No hot-oil circuit needed; simpler tooling and faster cycles
Shrinkage	~0.4–0.7%, relatively uniform	A first tool lands close to the drawing
Drying	Modest, ~80–90 °C, 2–4 h	Easy compared with PC or nylon
Tool attack	None	Ordinary mould steels are adequate
Flow	Good	Fills thin and complex sections reliably

The combination is why ABS appears in so many housings, covers, bezels and consumer products: the material does not fight the process, so the tool can be simpler, the cycle shorter, and the first shot closer to correct.

Amorphous shrinkage, and why it matters

ABS is amorphous — it has no crystalline structure. That has a direct effect on how it shrinks.

A semi-crystalline material like polypropylene or acetal shrinks substantially as its crystals form during cooling, and the amount depends on how the polymer chains oriented as they filled the mould. That produces differential shrinkage — different amounts in the flow direction and across it — and differential shrinkage is what warps a part.

ABS shrinks less and more uniformly because there are no crystals to form. So:

• Total shrinkage is low, around 0.4–0.7%
• Shrinkage is roughly the same in all directions, so warpage from differential shrinkage is limited
• A first tool usually lands close, needing less correction than a semi-crystalline part

It is not perfectly constant. Wall thickness, gate location, packing pressure and mould temperature all move it within that band — which is why shrinkage is agreed per drawing in DFM rather than read off a table.

Design rules that matter for ABS

The material is forgiving, but the part geometry still has to respect the process.

Keep the wall uniform. A thick section beside a thin one cools at a different rate and shrinks differently. The result is a sink mark over the thick region and warpage across the part. Where a design needs local thickness — a boss, a rib, a mounting pad — core the thick section out, or reduce it to roughly two-thirds of the nominal wall.

Draft the walls. 0.5° is the practical minimum and 1–2° is the working range. ABS releases reasonably well, so it does not demand generous draft on a smooth wall — but texture adds drag, and a textured surface needs more draft than a polished one. That is worth deciding before the texture is specified, because adding draft to a tool after it is cut is expensive.

Radius the corners. External corners should be radiused for appearance and internal corners for strength, since a sharp internal corner concentrates stress and is where a part will crack in service. A common rule of thumb is an internal radius of at least half the wall thickness.

Place the gate thoughtfully. Gate location sets where the material enters, how the flow fronts meet, and where the weld lines and the pressure drop land. On a visible part the gate choice is also a cosmetic decision, and on a part that has to be strong it decides where the weak line is.

Design for release. Snap fits, undercuts and closures are all possible in ABS, but they need either a mechanism in the tool or a flexible feature designed into the part. ABS is tough enough to make snap features work well; that is one of the reasons it dominates enclosures.

What the moulded part will not do

Two limits belong on the design review rather than the shop floor.

Temperature. A moulded ABS part is good to roughly 70–80 °C — the lowest service temperature in this range. Near a motor, a lamp, a power supply, a heatsink or a dark surface in direct sunlight, that ceiling is reached faster than the ambient temperature suggests. Once exceeded, the part softens and creeps.

Stiffness. At around 2,000–2,300 MPa, ABS’s modulus is roughly a tenth of aluminium’s. A moulded ABS part that carries load will deflect immediately and continue to deform over time. ABS is a housing and covering material, and it is excellent at that job. Where the part has to carry load, the material review happens before the tool is cut — because a tool is expensive to change.

Molding route

Plastic molding runs through our vetted partner network, managed under one quality process, while metal inserts and machined features are done on our own floor in Qidong City, Jiangsu Province, China. Mould tooling is quoted per drawing, and mould size, shot weight and gate count are reviewed before the tool is cut.

That structure matters on a part that combines plastic and metal. A housing with a machined metal boss or a threaded insert is not two separate purchases — the mould and the inserts come from the same drawing, so the fit between plastic and metal is planned before the tool is made. Moulding holds part-scale tolerances agreed per drawing in DFM; it does not match machined metal, which is why a critical bore, face or thread is normally carried by a machined insert rather than by the plastic itself.

Where the same geometry reads better as a machined part, we quote it that way on our own floor and let the numbers decide. The machined side of this material is covered on our ABS CNC machining page.

Where molding ABS is the right choice

• Enclosures, housings, covers and bezels in volume
• Complex geometry with walls, ribs, bosses and snap features
• Parts that need a texture or a specific colour, since both are easier to achieve in a mould than by machining
• Consumer and industrial products where cost per part at volume matters
• Parts with metal inserts, where the insert is machined on our floor and moulded in
• Any part where the net shape would waste most of a machined blank

Where molding ABS is the wrong choice

The volume does not justify a tool. Tooling is a fixed cost; below the volume where it amortises, machining is cheaper. Prototypes, revisions and low-volume parts are the machining cases.

The service temperature is above roughly 70–80 °C. ABS is the lowest in this range. Polycarbonate is the next step up.

The part carries load or must be stiff. ABS’s modulus is low and it creeps.

The part meets solvents, fuels or aggressive cleaning agents. ABS dissolves in ketones, esters and chlorinated solvents, and many common fluids soften it.

The part is outdoors long-term. Unstabilised ABS chalks, yellows and embrittles in sunlight; a stabilised grade is available, and for a long service life the material is usually reconsidered.

Transparency is required. ABS is opaque. Acrylic and polycarbonate are the transparent moulding materials.

What to put on the drawing

Instead of	Write
Plastic	ABS, for a housing or cover at volume
ABS, wall thickness	Specify the nominal wall and keep it uniform — say where local thickening is needed
ABS, textured surface	State it — texture needs more draft than a polished wall
ABS, metal insert	Say so — the insert is machined on our floor and moulded in
ABS, service temperature	State it — the limit is around 70–80 °C
ABS, carries load	Wrong material — low modulus, and it creeps
ABS, meets solvents or fuels	Name the chemical — ABS dissolves in many common fluids
ABS, outdoor service	Specify a UV-stabilised grade
ABS, low volume or still changing	Machine it instead — tooling is a fixed cost

The three lines that decide most ABS moldings are the wall thickness and how uniform it is, where the gate can sit, and what the part has to survive in service. The first two are the moulding review. The third decides whether ABS is the right material at all, and it is much cheaper to settle before the tool is cut.

Send the drawing through the request a quote form and the reply comes back within 24 hours with DFM feedback — including a note on the wall, the draft, the gate position and the material grade where any of them need settling, and a comparison against machining the same part where the volume is borderline.