Die Casting Process, Materials, Molds, Pros, and Cons | Neway

Die casting, a precision-driven and efficient metal manufacturing process, is a cornerstone in producing goods across industrial, commercial, and consumer sectors. Die-cast parts are renowned for their accuracy, making die-casting a go-to process for creating complex metal components, especially in high-volume production scenarios. The die caster often works with primary materials such as aluminum, magnesium, and zinc alloys, each offering unique benefits and being suitable for specific applications. This in-depth exploration of die-casting will provide valuable insights for designers and purchasers in the plastic injection molding industry, particularly those seeking custom die-cast parts.

Exploring the Various Types of Die Casting

Die casting is not a one-size-fits-all process. It branches into several types, each possessing unique characteristics and applications, catering to the needs of different die casters and their projects.

Hot Chamber Die Casting

This method involves melting the metal within a chamber directly attached to the die-casting machine. It's typically employed for metals with lower melting points, such as zinc, magnesium, and lead alloys. It is more suitable for the manufacture of small parts such as zinc alloy watch frames, belt buckles, and zinc alloy electronic cigarette cases.

Cold Chamber Die Casting

In contrast to hot chamber die casting, the metal is melted in a separate furnace before being transferred to the machine. This method is slower but is used for metals with higher melting points, like aluminum die cast alloys.

Die Casting Process Steps

Regardless of the die-casting type, the process follows a routine. Here are the steps involved:

Clamping

The initial stage involves readying the dies for casting. The two halves of the die, the cover die half, and the ejector die half, are secured together—the gap between these two halves functions as the mold cavity.

Injection

In the subsequent stage, molten metal is injected into the mold cavity under high pressure. The pressure degree depends on the material type and whether it is a hot-chamber or cold-chamber die casting machine. The pressure ensures that the material is forced into even the tiniest crevices of the mold.

Cooling

Post-injection, the molten metal begins to cool and solidify within the mold cavity. The pressure is maintained during this stage to mitigate shrinkage and ensure the metal fills the cavity.

Ejection

Once the metal has cooled and solidified, the casting is ejected. The dies are opened, and the castings are gently pushed out of the dies with ejector pins. Another shot can be prepared immediately after the ejection, enabling rapid mass manufacture of identical parts.

Trimming

The final stage of the die-casting process is the shakeout stage. This involves cutting the excess bits of metal attached to the casting, including flash from the parting line and any gates, runners, and sprues.

Understanding these steps is crucial for part designers and purchasers as it helps to plan the design and production process effectively.

Material Considerations in Die Casting

Die casting employs a variety of metals, predominantly non-ferrous, although occasionally ferrous metals can be used too. The primary die casting materials are aluminum, magnesium, and zinc alloys, each with unique properties and applications.

Aluminum Alloys

Aluminium die-casting alloys are lightweight and offer good dimensional stability, making them an excellent choice for complex, fine-featured parts. They also provide good corrosion resistance, temperature resistance, and thermal and electrical conductivity. 

Materials Selector

Commercial:	360	A360	380 b	A380 b	383	384 b	B390*	13	A13	43	218
ANSI/AA	360.0	A360.0	380.0	A380.0	383.0	384.0	B390.0	413.0	A413.0	C443.0	518.0
Nominal	Mg 0.5	Mg 0.5	Cu 3.5	Cu 3.5	Cu 2.5	Cu 3.8	Cu 4.5	Si 12.0	Si 12.0	Si 5.0	Mg 8.0
Comp:	Si 9.0	Si 9.5	Si 8.5	Si 8.5	Si 10.5	Si 11.0	Si 17.0

Chemical Composition

Detailed Composition
Silicon Si	9.0-10.0	9.0-10.0	7.5-9.5	7.5-9.5	9.5-11.5	10.5-12.0	16.0-18.0	11.0-13.0	11.0-13.0	4.5-6.0	0.35
Iron Fe	2.0	1.3	2.0	1.3	1.3	1.3	1.3	2.0	1.3	2.0	1.8
Copper Cu	0.6	0.6	3.0-4.0	3.0-4.0	2.0-3.0	3.0-4.5	4.0-5.0	1.0	1.0	0.6	0.25
Magnesium Mg	0.4-0.6	0.4-0.6	0.30 f	0.30 f	0.10	0.10	0.45- 0.65	0.10	0.10	0.10	7.5-8.5
Manganese Mn	0.35	0.35	0.50	0.50	0.50	0.50	0.50	0.35	0.35	0.35	0.35
Nickel Ni	0.50	0.50	0.50	0.50	0.30	0.50	0.10	0.50	0.50	0.50	0.15
Zinc Zn	0.50	0.50	3.0	3.0	3.0	3.0	1.5	0.50	0.50	0.50	0.15
Tin Sn	0.15	0.15	0.35	0.35	0.15	0.35	—	0.15	0.15	0.15	0.15
Titanium Ti	—	—	—	—	—	—	0.10	—	—	—	—
Others Each	—	—	—	—	—	—	0.10	—	—	—	—
Total Others c	0.25	0.25	0.50	0.50	0.50	0.50	0.20	0.25	0.25	0.25	0.25
Aluminum Al	Balance	Balance	Balance	Balance	Balance	Balance	Balance	Balance	Balance	Balance	Balance

 

Aluminum Die Casting Alloys
Commercial	360	A360	380	A380 EF	383	384	B390*	13	A13	43	218
ANSI/AA	360	A360.0	380.0	A380.0	383 E	384.0	B390.0	413	A413.0	C443.0	518.0
Mechanical Properties
Ultimate Tensile Strength
KSI	44	46	46	47	45	48	46	43	42	33	45
(MPa)	303	317	317	324	310	331	317	296	290	228	310
Yield Strength
KSI	25	24	23	23	22	24	36	21	19	14	28
(MPa)	172	165	159	159	152	165	248	145	131	97	193
Elongation
% in 2in. (51mm)	2.5	3.5	3.5	3.5	3.5	2.5	<1	2.5	3.5	9	5
Hardness b
BHN	75	75	80	80	75	85	120	80	80	65	80
Shear Strength
ksi	28	26	28	27		29		25	25	19	29
(MPa)	193	179	193	186	—	200	—	172	172	131	200
Impact Strength
ftlb	—	—	3	—	3 d	—	—	—	—	—	7
(J)	—	—	4	—	4	—	—	—	—	—	9
Fatigue Strength c
KSI	20    (MPa	18	20	20	21	20	20	19	19	17	20
(MPa)	138	124	138	138	145	138	138	131	131	117	138
Young’s Modulus
psi x 106	10.3	10.3	10.3	10.3	10.3	—	11.8	10.3	—	10.3	—
(GPa)	-71	71	71	71	71	—	81	71	—	71	—
Physical Properties
Density
lb/in3	0.095	0.095	0.099	0.098	0.099	0.102	0.098	0.096	0.096	0.097	0.093
(g/cm3)	2.63	2.63	2.74	2.71	2.74	2.82	2.71	2.66	2.66	2.69	2.57
Melting Range
°F	1035-1105	1035-1105	1000-1100	1000-1100	960-1080	960-1080	950-1200	1065-1080	1065-1080	1065-1170	995-1150
(°C)	557-596	557-596	540-595	540-595	516-582	516-582	510-650	574-582	574-582	574-632	535-621
Specific Heat
BTU/lb °F	0.23	0.23	0.23	0.23	—	0.23	—	0.23	0.23	0.23	—
(J/kg °C)	963	963	963	963	—	963	—	963	963	963	—
Coefficient of Thermal Expansion
u in/in°F			12.2	12.1	11.7	11.6	10	11.3	11.9	12.2	13.4
(u m/m°K)			22	21.8	21.1	21	18	20.4	21.6	22	24.1
Thermal Conductivity
BTU/ft hr°F	65.3	65.3	55.6	55.6	55.6	55.6	77.4	70.1	70.1	82.2	55.6
(W/m °K)	113	113	96.2	96.2	96.2	96.2	134	121	121	142	96.2
Electrical Conductivity
% IACS	30	29	27	23	23	22	27	31	31	37	24
Poisson’s Ratio	0.33	0.33	0.33	0.33	0.33	—	—	—	—	0.33	—

Zinc and Za Alloys

Zinc alloys are the most manufacturer-friendly of die casting materials and offer benefits like impact strength, ductility, and suitability for plating. Due to their castability, they also result in minimal die wear.

Copper Alloys

Copper alloys exhibit high strength, hardness, corrosion resistance, and excellent dimensional stability. 

Magnesium Alloys

Magnesium is even lighter than aluminum, with the advantage of being highly machinable. It is suitable for cast parts requiring additional details or machined surface finishing.

Geometry in Die Casting Design

Designing for die casting requires understanding several principles and considerations to ensure the final part meets the desired specifications and quality. Here are some key aspects:

Parting Line

The parting line is where the two halves of the die meet. The parting line's location can affect the die's complexity and the appearance of the final casting.

Draft

The draft is a slight angle incorporated into the walls of the part that are parallel to the opening direction of the die. This allows for easier ejection of the part from the die.

Fillet Radii

Fillets are the rounded corners and edges of the part. They help reduce stress concentration and improve the molten metal's flow.

Bosses

Bosses have raised portions of the design for mounting and other functional purposes. They should be connected to walls or ribs for better support and cooling.

Ribs

Ribs are thin, flat sections of the part that add strength and rigidity. They also help in improving the flow of the molten metal and cooling.

Holes and Windows

Holes and windows are openings in part. Their size and location can affect the molten metal's flow and the part's strength.

Tolerances in Die Casting

Die casting can achieve high precision and tight tolerances. However, the achievable tolerances can vary based on factors such as the type of material, the design of the part, and the specific die casting process used. Critical aspects of die casting tolerances include:

Linear Dimensions

These are the straight-line measurements of the part. They can be affected by factors such as the material's shrinkage and the die's thermal expansion.

Flatness

Flatness measures a surface's deviation from being perfectly flat. It can be affected by factors such as the cooling rate and the part's design.

Roundness

Roundness is the measure of how closely the shape of an object approaches that of a perfect circle. It can be affected by factors such as the flow of the molten metal and the cooling rate.

Surface Finishes in Die Casting 

What are the surface finishes of die castings, and how to achieve them? The surface finish of a die cast part can be influenced by the type of material, the design of the part, and the specific die casting process used. Several types of surface finishes can be achieved:

As Die-Cast Finishes

These are the finishes that are achieved directly from the die casting process. They can vary based on the material type and the die's condition.

Machining Finishes

These are finishes achieved through mechanical processes such as grinding, polishing, blasting, and buffing.

Chemical Finishes

These are finishes achieved through chemical processes such as etching, anodizing, and plating.

Powder Coating

These finishes involve applying a layer of paint or powder to the part's surface.

These are specialized finishes that can provide unique aesthetic or functional properties to the part.

Weighing the Pros and Cons of Die Casting

Die casting offers several advantages, making it a preferred choice for mass production of complex parts. However, it also has certain limitations that need to be considered.

Multi-Slide and Conventional Die Casting

Multi-slide die casting uses multiple slides in the tooling, allowing for complex and intricate parts to be produced. Conventional die casting, on the other hand, uses a simpler tooling setup and is more suited for simpler parts.

Benefits of Multi-Slide Tooling

Multi-slide tooling allows for producing complex parts with high precision and excellent surface finish. It also offers faster cycle times, leading to higher productivity.

Benefits of Conventional Tooling

Conventional tooling is more straightforward and less expensive. It suits more significant parts and materials requiring slower injection speeds.

Die Casting Vs. Investment Casting

While die casting is ideal for the high-volume production of complex parts, investment casting allows for producing parts with intricate details and an excellent surface finish. However, investment casting is slower and more expensive.

Die Casting Vs. Sand Casting

Die casting offers higher precision, a better surface finish, and faster production times than sand casting. However, sand casting is more flexible regarding design changes and more suited for more significant parts.

Cost Considerations in Die Casting

Several factors can affect the cost of die casting. Understanding these factors can help in making cost-effective decisions.

Die Casting Material Selection: The type of material used can significantly affect the cost. Materials with higher melting points require more energy and can wear out the die faster.

- Production Cost: The production cost includes the cost of melting the material, operating the die casting machine, and labor costs.

- Mold Cost: The cost of the mold can be significant, especially for complex parts. However, the mold can be used for a large number of parts, spreading the cost over the production run.

- Secondary Operations Cost: Any secondary operations such as machining, surface finishing, and assembly can add to the cost. 

- Finishing Cost: The cost of the final finishing operations such as painting, plating, or coating can also add to the cost.

- How to Reduce Die-Cast Cost: Cost can be reduced by optimizing the part design, selecting the most suitable material, minimizing secondary operations, and optimizing the production process.

Applications of Die Casting Across Industries

Die casting is used in many industries due to its ability to produce complex parts with high precision and excellent surface finish. Here are some of the critical applications:

Automotive Industry

Die casting is extensively used in the automotive industry to produce automotive die castings such as engine blocks, cylinder heads, and other components. The high precision and excellent surface finish offered by die casting make it ideal for this industry.

Electronics Industry

Electronics Industry die castings such as heat sinks, shielding cases, and other parts that require high precision and excellent thermal conductivity. 

Aerospace Industry

The aerospace industry uses die casting to produce parts that require high strength, lightweight, and excellent corrosion resistance.

Medical Industry

Die casting is used in the medical industry to produce medical die castings such as surgical instruments, medical devices, and hospital equipment.

Construction Industry

Die casting is used in the construction industry to produce construction die casting parts such as door handles, window frames, and other hardware.

A Versatile and Efficient Manufacturing Process

Die casting, with its ability to produce complex parts with high precision and excellent surface finish, is a versatile and efficient manufacturing process. Whether it's aluminum die casting, zinc alloys, or other materials, die casting offers a range of benefits that make it a preferred choice for many industries.

Die casting is crucial for producing high-quality automotive, electronics, aerospace, medical, and construction parts. With advancements in technology and materials, the potential applications of die casting are continually expanding.

For purchasers and designers seeking custom die-cast parts, understanding the intricacies of die casting – from the process and materials to design considerations, tolerances, surface finishes, and cost factors – is essential. This knowledge will enable them to make informed decisions and leverage the benefits of die casting to meet their specific requirements.

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