Assembly Methods for Die Cast Parts

Assembly Methods for Die Cast Parts

Die casting is an extremely popular manufacturing process for creating metal products. Die cast parts produce high quality, uniform pieces that can be created in just about any size, part geometry, surface texture, or finish. They can require minimal secondary processes since many features can be integrated into the design such as studs, hinges, drill holes, and bosses, to name a few. There are quite a few methods to assemble individual die cast parts made from aluminum or zinc.

These methods include:
• Adhesive bonding
• Attachment systems
• External threads
• Forming or self-cutting fasteners
• Injected Metal Assembly (IMA)
• Inserts
• Interference fits
• Threaded fasteners

Adhesive bonding
Adhesive bonding between metals is becoming a more popular practice among die casters. The adhesive “wets” the entire surface to be joined and must have a lower surface tension than the materials being joined. Joints that are subjected to high tension are generally not suitable for adhesive bonding. Adhesive bonds are also prone to thermal degradation and peeling. Adhesive bonding is extremely popular for bonding sheet steel in automobile bodies.

Attachment systems
Attachments that require plastic deformation of the casting is usually limited to alloys with high ductility, such as zinc.

Attachments of this nature include:
• Crimping
• Staking
• Swaging

Adhesive bonding has become much more popular since the stresses are spread out more uniformly and exposed surfaces are not disturbed. They also offer other benefits such as sealing, insulating, and corrosion barriers.

External threads
It is possible to cast external threads on cylindrical features under specific circumstances. Threads can be formed across the parting line of the die with either slides or solid components. Flash can get left in threads with slides, or made across parting lines, which can be quite difficult to remove. If the flash isn’t severe, it can be removed through the process of the bolt and nut installation. Many manufacturers prefer casting flats at the root of the thread on the parting line so that the flash forms on the flats making it very easy to remove.

Forming or self-cutting fasteners
This type of assembly utilizes hard steel fasteners that anchor to the die cast part itself by either forming to or cutting into the part as they are installed. Die cast alloys are typically relatively soft and readily accept these types of fasteners.

These types of fasteners include:
• Spring clips
• Stamped nuts
• Self-tapping screws
• Thread-forming screws

In most cases properly sized holes can be cast into the part to accept the required fastener. Spring clips and stamped nuts develop a relatively low retention force where as self-tapping and thread-forming screws have a much higher retention capability. Though, fasteners that cut form small chips where they bite into the metal part which may not be tolerable in certain finished projects, such as sensitive electronic equipment.

Injected Metal Assembly (IMA)
The IMA process is very similar to the adhesive bonding process except IMA utilizes a molten alloy to bond components together. The process creates a strong, permanent, mechanical “lock” that can withstand high loads and can also bond metals to non-metal parts. The process requires no special surface preparations and issues such as thermal degradation and peeling are not very common.IMA bonds also perform exceptionally well in harsh environments.

Small components of just about any material can be joined utilizing IMA, such as:
• Ceramic
• Elastomers
• Fibers
• Metals
• Paper
• Plastics

Inserts
Inserts are used when the design will impose conditions that exceed the capabilities of the alloys such as excessive thread wear, concentrated loads, abrasion, and wear at a bearing point. However, inserts cause residual stress within the cast part so proper planning for long term retention is vital. There are two types of inserts that can be installed – cast-in-place or post-installed inserts. The cycle time and the cost are usually what determine which type of inserts is used.

Cast-in-place inserts allow for a wider range of mechanical lock securing options since the alloy is cast directly around the insert. They are required to be as dimensionally accurate as the die into which it is inserted, which increases both the cycle time and cost per part. However, with very large castings it is more economical to use cast-in-place inserts since the cycle time is already increased due to the size of the cast part.


Examples of cast-in-place inserts

Post-installed inserts are more economical for faster run, smaller parts produced on highly automated machines and projects which have less stringent tolerances.

Interference fits
These types of fits are used to retain components, such as bearing and dowel inserts. If the interference is light (0.001 in./in [0.001 mm/mm] or less), the installation can take place with both parts at room temperature. Heavy interference usually requires the parts to be heated and may also cause metal removal which will lead to a reduction in retention. The removal of metal on the parts depends on the hardness of the metals, the amount of interference, lubricant use, and the leading edge of each part.

Threaded fasteners
Threaded bolts, or studs, are commonly used to join die cast parts together. If the attachments are made in sections with thin walls clearance holes are needed in order to allow the bolt to pass through. The bolt would then be secured in place with a nut.

Bosses are capable of being designed into the casting itself to receive bolts or studs into tapped holes. Though the boss diameter will need to be at least twice the size of the bolt’s diameter since die cast joints are more prone to dilation.

Also, keep in mind that in order to minimize porosity in the cast area where the thread is present, the tapped holes need to be cored. Both coarse and fine threads can be tapped although coarser threads are generally preferred.

The process of die casting and any secondary assembly operations have a symbiotic relationship; meaning they are heavily dependent upon each other and they work together to create the final product. Planning ahead for the assembly method you will use can help to minimize any potential problems as well as reduce costs and speed up production time.

Need a hand? With over 75 years of die casting expertise, our team of experienced engineers will evaluate your requirements to help you decide which would be the best fastener option to join your components to achieve the desired result for your part. Our in-depth knowledge and experience allows us to control the entire pre- and post-operative processing, as well as provide turn key part solutions with a variety of options, to meet our customer’s individual needs. Contact A&B Die Casting today to get started on your next project!

Die Casting with Zinc – Versatility with Economy

Die Casting with Zinc – Versatility with Economy

Zinc is a casting alloy that offers high precision with lower tooling cost for small parts. Zinc’s superior strength and hardness is an ideal alternative for machined, pressed, stamped, and fabricated components. Zinc is optimal for complex net shaped parts with thin walls while offering excellent electrical performance and shielding properties. Its structural integrity and wear-resistance are optimal for creating multi-faceted, complex shapes with a versatile range of physical, mechanical, and finishing characteristics.

The advantages of zinc die casting include:
• Complex shapes with thin walls
• Superior mechanical and physical properties
• Excellent tensile strength and dimensional stability
• RFI/EMI shielding capabilities
• Long die life
• Superior as-cast cosmetic finish

Zinc alloys are optimal for casting parts requiring intricate detail and close dimensional tolerances at high production rates. Zinc alloys are castable to closer tolerances than any other metal or molded plastic. Zinc casting alloys are stronger than reinforced molded polymers and zinc’s hardness, self-lubricating properties, dimensional stability, and high modulus make is suitable for working mechanical parts (such as gears and pinions).

For parts requiring hardness, high durability and cosmetic finishes, zinc die casting provides an economical solution while offering:
• High strength and hardness
• Excellent electrical conductivity
• High thermal conductivity
• Low raw material cost
• High dimensional accuracy and stability
• Excellent thin wall capability
• Cold Form capabilities to ease joining
• High quality finishing characteristics
• Outstanding corrosion resistance
• Full recyclability

Zinc also has excellent thermal and electrical conductivity, as well as precise casting tolerances, which makes it an ideal material choice for heat sinks, electrical components and applications that require electromagnetic shielding.

Zinc can be cast at moderate temperatures which provide significant energy and processing savings over other metals and engineering alloys.

The ease of use in die casting combined with high precision and lower tooling make zinc a top choice for designers from nearly any industry. Contact A&B Die Casting today to get started on your next project!

What Finish Is Right For Your Die Cast Parts? Part 3 | The Finishes that A&B Die Casting Specializes In

What Finish Is Right For Your Die Cast Parts? Part 3 | The Finishes that A&B Die Casting Specializes In

Once a part has been die-cast the process is not quite over. Die cast part finishes are intended to improve the aesthetic and functional characteristics of your component. There are an extremely large number of finishes out there to choose from and the surface finish affects both the appearance and performance of the item. They include everything from finishes that add a decorative touch to the product to others that improve the part’s chemical or corrosion resistance.

A finish is not always essential but it can be a crucial factor in the die casting process since the design of the piece needs to take the finish into consideration to ensure that your final product meets all dimensional requirements. Each step of the die casting process has an impact on the final product. Specific features such as parting lines, vents, ejector pins, and gates need to be taken into consideration early in the design phase to determine the most effective placement so that they don’t interfere with the purpose of the finish.

High quality surface finishes are necessary for things like:
• High shine decorative finish
• Protection against environmental exposure
• Resistance to wear
• Insulation from galvanic corrosion
• And more

Over the last couple of months we have talked at length about finishes in more broad terms and now we want to complete this series by discussing the most popular finishes that we work with. This will help you to find well received finishes, know what they are, and give you the information that you need to find a finish that may be a bit more unique for your product. So, what specific surface finishes do we specialize in?

Decorative:
• Powder coating
• Wet Painting
• Ceramic Coating
Electro Plating

Semi-Decorative:
Electroless Nickel Plating
• Brushed Metal Finishing
• Ball Burnishing

Non-Decorative:
• Chemical Conversion Film
• Anodizing
• Sand Blasting
• Vibratory Finishing

Our standard finishing steps include:
1. Deburring and post-cast processes to remove loose flash, round sharp edges, smooth and brighten surfaces. We use both automated vibratory deburring and mechanical deburring methods to achieve the required finish.
2. Coatings for function including sealing, protection against corrosion, heat dissipation, surface performance and insulation. Most coatings are either paint or plating based.
3. Cosmetic and decorative coatings require a refined approach in both die casting processes and post casting finishing processes. The quality of the finish is directly affected by the quality of the surface underneath.

In general, plating processes are the poorest at hiding underlying surface conditions and require the most surface prep operations to achieve the desired final finish. Due to the fact that a die cast part needs to be heated during certain decorative finishing processes (such as plating and painting), it is vital for the die cast part to have both a good internal structure and good surface finish. These are achieved through good design for both the tool and the component as well as the proper post-casting operations to achieve the optimum surface finish for the desired final plating result.

The process of die casting and following die casting finishes have a symbiotic relationship; meaning they are heavily dependent upon each other and they work together to create the final product. Planning ahead for the finish you need can help to potentially minimize surface finish problems as well as any potential porosity issues. As you can see A&B Die Casting offers a wide range of options and also works closely with you to discover the perfect finishing solutions for your parts.

Our in-depth knowledge and experience allows us to control the entire pre- and post-operative processing, as well as provide turn key part solutions with a variety of options, to meet our customer’s design requirements which ensures that we achieve the desired end product. With over 75 years of die casting surface finishing expertise, our engineers will evaluate your requirements to recommend the best approach to achieve the desired finish for your part. Contact A&B Die Casting today!

What Finish Is Right For Your Die Cast Parts? Part 2 | Electroplating & Electroless Plating

What Finish Is Right For Your Die Cast Parts? Part 2 | Electroplating & Electroless Plating

A die casting surface finish can provide durability, protection, and an attractive appearance. Last month we detailed the most common decorative finishes used in the industry – this article will delve a bit more into two types of plating that can be applied to die castings; electro-plating or electroless plating. What is the difference between the two processes and which would work best for your application?

Electroplating
Electroplating is a process where thin layers of metal are bonded at the molecular level with another metal. An electrical current is passed by two electrode terminals through a carefully prepared electrolyte solution where a metal part has been placed for plating. The electricity changes the surface properties of the part and allows it to bond with the metals in the electrolyte solution.

What types of metals can be plated this way?
• Platinum
• Gold
• Silver
• Chromium
• Copper
• Tin
• Aluminum*
• Zinc
• Cadmium
• Nickel
• Lead

*Aluminum has a tendency to form an oxide that may prevent proper plating adhesion. It is best to apply a zinc undercoating to aluminum parts before any type of plating.

Why choose electroplating?
• Improve appearance
• Improve the abrasion and wear resistance
• Corrosion protection
• Increase lubricity
• Increase the thickness of a part

What parts are commonly electroplated? Here are a few examples:
• Tools and dies
• Aircraft components
• Machine components
• Mechanical assemblies
• Electronics and computer devices
• Enclosures, chassis, and heat sinks
• Medical diagnostic instruments
• And many more

Electroplating is capable of achieving the best cosmetic plating finish on die castings, since multiple layers of plating are applied and buffing/polishing can be performed after each layer. The main downside to electroplating is that it is very difficult to properly and evenly plate parts with complex shapes. The electroplating process also requires very clean conditions, utilizes possibly hazardous equipment, requires filtration, and typically requires multiple applications to achieve the desired look and thickness. In some instances electroless plating is the better alternative.

Electroless Plating
Electroless plating is quickly becoming one of the most widely used forms of plating today because it is more cost-effective and easier to do than electroplating. Electroless plating is used primarily as a protective and/or used to enhance electrical conductivity. In some cases, it can also be used as a decorative coating.

Electroless plating is also known as autocatalytic plating or conversion coating. Simply put, it is a process for plating a part without using an electrical current. The process for electroless plating basically involves dipping a part into a bath of plating solution where a reducing agent (like hydrated sodium hypophosphite) reacts with the ions in the part to deposit another metal alloy onto it (typically nickel).

A wide variety of metals can be plated this way, including (but not limited to):
• Aluminum
• Titanium
• Mild steels
• Stainless steel
• Hardened steel
• Copper
• Brass
• Zinc

Why choose electroless plating?
• Prevents corrosion and wear
• Adds toughness
• Resistance to abrasion
• Uniform deposits with consistent thickness
• Can be used on parts with very complex shapes

Due to the fact that electroless plating tends to create a very hard and non porous finish, this technique is very popular in industries such as oil fields or marine applications where parts are very vulnerable to wear and corrosion.

What other industries commonly use electroless plating? Here are a few examples:
• Oil and gas – barrels, pipes, pipe fittings, valves
• Automotive – gears, brake pistons, shock absorbers, cylinders
• Food service – food processing machine parts, molds
• Plastics and textiles – dies, machine parts, molds, extruders
• Aerospace – rocket parts, pumps, valves, pistons
• Chemicals – mixing blades, filer units, pumps, heat exchangers
• And so many more

In general, plating processes are the poorest at hiding underlying surface conditions and require the most surface prep operations to achieve the desired final finish. It is vital for a die cast part to have both a good internal structure and good surface finish. These are achieved through good design for both the tool and the component as well as the proper post-casting operations to achieve the optimum surface finish for the desired final plating result. Planning ahead for the finish you need can help to potentially minimize surface finish problems as well as any potential porosity issues.

With over 75 years of die casting surface finishing expertise, our engineers will evaluate your requirements to recommend the best approach to achieve the desired finish for your part. Contact A&B Die Casting today!

What Finish Is Right For Your Die Cast Parts? Part 1 | Decorative

What Finish Is Right For Your Die Cast Parts? Part 1 | Decorative

A die casting surface finish can provide durability, protection, and a decorative appearance. Over the next few months we will explore different types of finishes and how they are beneficial for different types of die cast parts.

Due to the fact that a die cast part needs to be heated during decorative finishing processes (such as plating and painting), it is vital for the die cast part to have both a good internal structure and good surface finish. These are achieved through good design for both the tool and the component. Planning ahead for the finish you need can help to potentially minimize surface finish problems as well as any potential porosity issues.

Types of decorative finish:
• Smooth and Shiny: In cases where a smooth and shiny surface is required, the density of the casting itself must be higher so that the part can be plated and buffed repeatedly. This type of finish requires the most preparation of the casting to achieve a smooth surface under the coating. Smooth and glossy finishes have the least ability to hide any surface imperfections.
• Satin and Textured: For satin finishes, brushing or media blasting can be used to achieve the desired surface finish before coating.

The 5 Most Common Decorative Finishes:
1. Painting
2. Powder Coating
3. Antiquing
4. Ceramic Coating
5. Plating

1.) Painting

Painted

Lacquers, paints, and enamels can easily be applied to die cast parts and work for both decorative and protective purposes. As with any finish, special considerations must be taken at the design stages of the part to plan for the type of painting finish you need. Precautions are taken in order to remove any oils from the cast surfaces. For best results, a conversion coating is applied after cleaning to ensure good adhesion of the coating to the die cast surface.

2.) Powder Coating

PowderCoating

Powder coating is commonly used as a decorative finish because it is able to hide minor flaws in the surface, the thickness is better controlled and more uniform, it is quite durable, very glossy, and has great color consistency and vibrancy. Powder coating yields a very hard, high anti-corrosion finish which makes it better at resisting dings and scratches. Unlike paints, powder coating reaches its final cured hardness during the baking cycle. Paints continue to cure for a period of time after baking, which may cause a delay in subsequent assembly operations. Powder coating is also quite environmentally friendly because the process produces no hazardous air pollutants or waste byproducts.

3.) Antiquing

Antiqued

In order to create an antique look, zinc castings electroplated with copper (or any other of its alloying agents), can be covered in a layer of colored components, such as copper sulfide. This casting is then ‘relieved’ – a process which entails the removal of some of the colored layers on highpoints in order to present the underlying layer of the yellowish brass or the reddish copper. The parts are then treated with lacquer in order to prevent tarnishing.

4.) Ceramic Coating

Ceramic

Ceramic coatings provide a very thin and decorative coating for die castings. Similar in thickness to anodizing, ceramic coatings can be applied to the entire part surface and in some cases even internal threads can be coated. Since the coating is very thin, any surface imperfections in the die casting will show through. Care must be taken with surface prep operations to ensure the desired final finish is achieved.

5.) Plating

Plating

Plating can be applied to die castings using either the electroless or electro-plating processes. Electroless plating is used primarily as a protective and/or used to enhance electrical conductivity. In some cases, it can be used as a decorative coating. Electro-plating is capable of achieving the best cosmetic plating finish on die castings, since multiple layers of plating are applied and buffing/polishing can be performed after each layer. In general, plating processes are the poorest at hiding underlying surface conditions and require the most surface prep operations to achieve the desired final finish.

With over 75 years of die casting surface finishing expertise, our engineers will evaluate your requirements to recommend the best design and finishing options. Contact A&B Die Casting today!