M&PII: Processes Quiz 3

Contact Molding Benefits

Flexible for complex/custom shapes - ideal for large or one-off parts

Low tooling/capital cost - inexpensive molds and minimal equipment

Contact Molding Disadvantages

Labor-intensive - high per-unit cost for manual lay-up

Low repeatability/precision - inconsistent thickness and fiber distribution

Contact Molding Comparison

VARTM (Vacuum-Assisted Resin Transfer Molding): Fibers placed in a closed mold and resin pulled through under vacuum

Contact Molding Tolerances

±0.125" to ±0.200" (typical for hand lay-up contact molding)

Contact Molding Product

Pro-line boat hulls

Large, complex curved hulls made with hand-laid fiberglass

Offers smooth gelcoat finish, corrosion resistance, and structural strength at low tooling cost

Transfer Molding Benefits

More precise than compression molding

Can be used to make medical equipment because of production can be sterile and with biocompatible components.

Dimensional consistency across batches

Transfer Molding Disadvantages

Slower production rate as it is more labor intensive compared to injection molding.

Cost of the actual mold to make the product is incredibly expensive ($12,000-$100,000)

Waste of material is largely created during the process

Transfer Molding Comparison

Injection molding

Transfer Molding Tolerances

Larger parts - 0.0039″

Smaller parts - 0.00098"

Transfer Molding Product

O-Rings

Insert Molding Benefits

Much more durable since plastic pieces are stronger with other components

One step process required for the actual molding process

Good for smaller molded pieces vs blow molding which is not able to achieve the same detail or strength

Insert Molding Disadvantages

Custom metal inserts can be pricey depending on the manufacturing methods

Making sure the materials work well together can be difficult vs using a process with just one material or multiple plastics like blow molding or overmolding

Insert Molding Comparison

overmolding

- This often uses different plastics to create grips and improve overall aesthetics of a component or tool lik shock absorption, insulation, and ergonomics

Insert Molding Tolerances

±0.001"-0.005"

Insert Molding Product

Screwdriver

Investment Casting Benefits

Allows for metals/alloys with significantly higher melting points to be used

Allows for undercuts to be made economically

Investment Casting Disadvanatges

It's multi-step process makes the cycle time incredibly long

It is often limited to parts under 75lbs.

Investment Casting Comparison

Metal Injection Molding: Powdered metal and binder are melted and shot into a mold. The binder is then sintered off to leave the metal behind.

Investment Casting Tolerances

.003" for parts under 1", with .003-.005" per additional inch.

Investment Casting Product

Turbocharger scroll

Die Casting Benefits

Intricate components with excellent dimensional accuracy, compared to injection moulding.

Excellent surface finish, reduces post machine time and added costs, compared to Sand Casting

Die Casting Disadvantages

High investment and operating costs, compared to CNC machining where a smaller number of parts can be produced more cost-effectively.

Die-cast weight limited by the locking force of the machine, unlike Sand Casting with no locking force.

Die Casting Comparison

similar process to Metal Injection Molding, but is more suitable for metals with low melting points and no sintering is required.

Die Casting Tolerances

Small parts: ±0.004 in

Large parts: ±0.01 in

Smooth finish: ~1-2 µm Ra, minimal machining needed

Die Casting Product

Matchbox cars

Multi-Shot Molding Benefits

Stronger bond between materials and higher production efficiency than overmolding

Multi-Shot Molding Disadvantages

Higher capital cost than overmolding and a required material compatibility

Multi-Shot Molding Comparison

Overmolding - where a base part is molded first (or separately), then placed into a second mold for a subsequent material to be molded over it.

Multi-Shot Molding Tolerances

+/- 0.005 inches

Multi-Shot Molding Product

rubber tool handle