Zinc die casting is one of the favourite manufacturing processes that are commonly employed to make high-dimensional, complex-shaped precision metal parts that have finishes of high quality. It finds extensive use in the automotive, electronic, hardware and consumer goods industries. Zinc has got the intrinsic characteristics that include low melting temperature, high fluidity and corrosive resistance which make it a good material in the manufacture of precision components. Nevertheless, zinc die casting necessitates a keen consideration of a number of factors whenever developing designs that are strong, precise, and cost-effective parts. This paper will discuss necessary design consideration of precision zinc die-cast components.

Learning about Zinc Die Casting

Zinc turnat sub presiune is a process that entails the injection of molten zinc into a mold or die made out of steel in high pressure. As soon as the metal is solidified, the die is opened, and the part is ejected. Complex shapes with high tolerances can be produced quickly using the process. The common zinc alloys include Zamak 2 and Zamak 3 as well as Zamak 5, which provide high mechanical strength, resistance to corrosion as well as easy machining.

Zinc die casting has such benefits as:

• Finisaj de suprafață bun: Smooth finish which in many cases do not need much post-processing.
• Geometrie complexă: Has the capability of creating thin walls, ribs, bosses and threads.
• Mechanical and structural Strength and durability: suited to mechanical and structural use.

To achieve full benefit of these, best practices in part design are necessary by the designers.

Wall Thickness Guidelines

The management of the thickness of the walls is one of the most significant elements of zinc die casting design. Having equal wall thickness is important to avoid porosity, shrinkage, or warping defects.

Wall thickness recommendations:

• Minimum thickness: 0.5 – 0.7mm very small precision parts.
• Maximum thickness: 6 mm in order to prevent shrinkage.
• Uniformity: Maintain uniformity on the thickness of the wall. Do not make the sudden changes in the thickness, as it leads to uneven cooling and stress concentrations.
• Ribs and supports: Ribs are required to strengthen thin areas as opposed to thickening walls. The rib thickness is generally 4060 percent of the wall thickness.

Correct wall thickness guarantees structural strength, enhances the flow of metals and minimizes the potential of defects.

Unghiuri de proiectare

Draft angles are small inclinations that are provided on the vertical sides of a die-cast component to ease the action of extraction out of the mold. Without correct draft, components can adhesively stay on the die and result in defects or damages of the surface.

Recommendations on draft angle to be used in zinc die casting:

• Vertical walls: at least 1 – 2   draft.
• Deep ribs or bosses: a draft of 0.5 -1, or 1, can be sufficient.
• Textured surfaces: Draft must be raised by 0.5-1 o to enable easy ejection.

Adequate draft angles minimize the wear of tools and enhance the production efficiency.

Bosses and Holes

Precision parts often have bosses and holes, which may be used to mount or fasten or assemble. Their design also plays a major role on the quality of casting.

Boss design guidelines:

• Wall thickness at bottom: 60 – 80 percent of nominal wall thickness.
• Height to diameter ratio: this is to be kept at a ratio of less than 3:1 to avoid contraction.
• Fillets: Place large fillets (0.5 -1 mm) at the bottom to eliminate the concentration of stress.

Hole design guidelines:

• Minimum hole diameter: small holes smaller than 1.5 mm – small holes are likely to fill defects.
• Location: Location of holes should not be too near to the wall or other bosses.
• Threads: Threaded inserts should be used instead of making fine threads in one piece so as to be strong and durable.

Compliance with these guidelines has a guarantee that the functional features can be made and reliable.

Ribs and Supports

Structural features To enhance strength, rigidity and dimensional stability of zinc die-cast parts, ribs and supports are added without unduly increment of wall thickness. They are needed when required to be precise parts with thin walls, and mechanical strength needs to be preserved.

Purpose of Ribs

• Stiffen thin walls: Ribs are not made, but make walls (where strength is required) stronger.
• Minimize distortion: Ribs eliminate the deformation in the process of cooling and handling.
• Support bosses: and mounting points: The ribs reinforce spaces in which screws or other fasteners have been laid.
• Enhance dimensional stability: Ribs serve to eliminate the chance of the part becoming out of shape.

Design Guidelines for Ribs

• Height: The ribs will normally be 23 times the nominal wall thickness. The filling or shrinkage could arise due to taller ribs.
• Grosime: The thickness of the ribs must be 40-60 percent of the thickness of the nearby wall. Sunk marks Fickers on visible surfaces may occur due to thick ribs.
• Spacing: Spacing between ribs should always be at least 213 times the wall thickness to ensure that they do not get interfered with during the mold filling and also to avoid defects.
• Fillets: Fillets should be added at the bottom of ribs (0.5-1 mm) to enhance flow of metals as well as a reduction in stress concentration and cracks.
• Proiectul unghiuri: Use a slight draft (0.5 -1 ) on the ribs, to enable them to be ejected out of the die.
• Unnecessary ribs: Only have ribs where necessary to provide structural support since additional ribs can make up more complicated dies which can be more expensive.

Examples of Rib Placement

• Under thin walls: Sagging or bending in the process of solidification can be stopped by ribs.
• Around bosses: It is possible to wrap a boss with ribs making threaded features or mounting features stronger.
• Through long, flat surfaces: Ribs will help stop warping of wide and flat surfaces and will keep the thickness of the wall unchanged.

Zinc die-casting uses proper design of ribs and supports that enhance precision, reduce weight, and cost of material. These are designed attributes that have to be critical, and that they must be durable, dimensionally accurate and defect free.

Corners and Fillets

The design features of zinc die-cast parts are corners and fillets. They determine the strength of the part, manufacturing convenience and the general appearance. Some of the issues that are caused by sharp ends include stress points, poor metal flow, and shrinkages. The part quality, durability, and the life of the tool are improved by using the fillets, smooth and rounded transitions between the surfaces.

Why Fillets Matter

• Minimise stress points: Angular internal corners are likely to crack. Fillets redistribute the stress over the part.
• Increase metal flow: Rounded corners enable the molten zinc to fill the die without having any chances of a void or an incomplete part.
• Reduce problem of shrinkage: Sudden increase and decrease in wall thickness may result in uneven cooling. In order to reduce imperfections, fillets make transitions less jagged.
• Enhance part strength: Rounded corners will ensure that the part does not break during handling, assembling, or daily operations.

Recommendations in Corner and Fillet design

Internal corners:

• Radius recommended: 0.5 -1.5 of the wall thickness.

Fatter radios are useful on thinner walls or those that are under greater stress.

External corners:

• Radius: 0.25 to 0.5 the wall thickness is recommended.
• Rounded edges enhance quality of surface and decrease wear of die.
• Fillets at ribs and bosses:Fillets should always be included at the junction of ribs and walls or bosses. This is to prevent sink marks and proper flow of metal.
• Avoid sharp edges:Acute parts may harm the die and chip when ejecting. Rounding in the edges is also easy to handle.
• Consistență:Keep equal radii throughout part. This makes the die design simple and assists in keeping the cooling homogeneous.

Practical Tips

• Make gradual change of geometry in place of sharp change.
• Ensure fillets do not get stuck in functional parts such as threads, slots and mating surfaces.
• When you must have a sharp corner, you can always smooth it off with a later machining operation instead of bending it in the casting.
• Zinc die-cast parts are more reliable, easier to make and designed properly corners and fillets make them stronger. 
• They also minimize defects, increase the life of dies and enhance the overall quality of the product completed.

Surface Finishes of Zinc Die-cast Parts: Procedures

Depending on functional and aesthetic needs, zinc die-cast objects can obtain a great variety of surface finishes. A proper choice of finishing technique increases the product image, prevents the corrosion of the part, and provides high functioning in assemblies.
The most common ways of finishing zinc die-cast parts are as follows:

Lustruire

Zinc die cast parts are polished to a smooth and shiny surface. It eliminates small flaws, enhances the surface of appearance and also the part is ready to be coated or plated. Depending on the complexity of the part, polishing may be done manually or by automated machines.

Utilizări: Decorative elements, visible elements or precision functional elements.

Placare

Plating is the deposition of a metallic coating, i.e. nickel, chrome or copper, on the part. This does not only enhance looks but also gives it resistance to corrosion and wear protection.

Puncte cheie:

• Chrome plating is mostly used on automotive and hardware components.
• The nickel plating provides a smooth and strong surface.
• Before plating, it is necessary to clean or polish the surface.

Acoperire cu pulbere

Powder coating is used to apply dry powder which is cured in heat creating a durable and hard surface. It offers a high standard of corrosion protection, chemical resistance and color range. Powder coating is particularly applicable to those parts that are faced with harsh environments.

Aplicații: Outdoor hardware, automotive parts and consumer electronics.

Pictura

Coating is also a low-cost way of enhancing the aesthetics and resistance to corrosion. Liquid paints can be used in a number of colors and can be selectively used in a single location rather than a powdered coating which cannot be applied selectively.

Aplicații: Decorative consumer product or parts where a color coding must be used.

Electrochemical Surface Patterning Technology

Anodizing is more popular in the case of aluminum but zinc parts may also be subjected to chemical surface treatments to enhance corrosion and surface hardness. Durability and paint adherence is improved using treatments such as chromate conversion finishes or passivation.

Texturare

Texturing provides a surface to the part that is matte or patterned. This may conceal small casting flaws, minimize glare and give handles or housings a superior grip.

Methods:

• Sandblasting
• Gravură chimică
• Die design texturing of molds.

Surfaces Finishing Practicals

• Keep in mind the requirements of surface finish when part is being designed to prevent any expensive rework.
• Select the finishing method that will be used according to the level of functioning, surrounding and outlook.
• Use a combination of finishing, where required, e.g. polishing and then plating can provide a combination of smoothness and corrosion resistance.
• Keep the thickness of the walls and fillets the same so that their surface will be the same when finished.

Design for Ejection

The cast part is to be removed out of the mold; this is known as ejection. Sticking, warping or surface blemishes can be caused by improper design.

Designing in a manner that can easily be ejected:

• Insert sufficient draft angles.
• Deep undercuts should only be made with the aid of side actions or slides during the die.
• Locate parting lines in such a way that the number of defects is reduced.
• Make the thickness of the walls consistent so that the shrinkages are not uneven.
• The design stage of thinking about ejection saves the cost of developing the tools.

Evitarea adânciturilor

Undercuts are those regions of the part geometry that can not be easily ejected out of the die. Although it is inevitable in some cases, undercuts make tooling more difficult, and expensive.

Guidelines:

• Redesign characteristics to do away with undercuts where possible.
• In case undercuts are needed then side actions, lifters or collapsible cores can be used.
• Undercut depth and area should be kept to a minimum in order to minimise complexity.
• Undercuts are avoided making it easy to design the die and less problems in production.

Toleranțe

Close dimensional tolerances are usually necessary in precision parts. Zinc die casting is very precise and there are certain things I would need to consider in design.

Tolerance tips:

• General dimensional tolerance:Small to medium parts:+-0.1-0.2mm.
• Critical dimensions: Clamping after casting with machining.
• Shrinkage allowance: Design: Since the shrinkage typically ranges between 0.5 and 1.5 percent depending on the size of the part, it should be designed with that in mind.

Effective tolerance planning is used to make sure that parts fit and that they work as expected.

Shrinkage and Control Warpage

When molten zinc is solidified, shrinkage takes place resulting in dimensional changes or voids. The warpage may take place when the walls are not straight or the ribs are poorly developed.

Guidelines:

• Keep wall thickness uniform.
• Provide support with the help of ribs and gussets.
• Large flat surfaces should be avoided; slight curvature is to be added in order to relieve warping.
• Thick layers on positions that are not vital.

Shrinkage and warpage are taken care of and this minimizes rejection and also guarantees quality.

Selectarea materialului

Selection of Zinc alloy is important to part performance. Common zinc alloys:

• Zamak 2:Good corrosion resistance, high strength, structural parts.
• Zamak 3: This is the most commonly used, it is a good corrosion and good mechanical properties.
• Zamak 5: Strength is increased, the thinner walls and tiny fine parts.

The choice of the alloy guarantees the best mechanical properties and castability.

Considerații privind costurile

• Design has an impact on the cost of die-cast parts of zinc:
• Geometries could be complex, which raises the cost of tooling.
• The high differences in the wall thickness cause defects and scrap.
• More die mechanisms are required in undercuts.
• Close tolerances can be machined secondarily.

Tradeoff between complexity and manufacturability of design will lower costs and not quality.

Zinc die-casting: What is the future of zinc die-casting?

The future of the zinc die-casting looks bright, and more precise, more automated and environment-friendly processes are made. Firms are also targeting to manufacture less weighty, more vigorous and more sophisticated components with less production waste and consumption of energy. Design software and surface finishing methods are also creating quality and efficiency through innovations.

What is the future strategy of GC Precision Mold?

To provide the future demands in the industry, GC Precision Mold focuses on the modern technology, the level of expertise and the use of modern machinery. Our philosophy is to be innovative, sustainable and provide even greater accuracy parts to changing markets.

Concluzie

Die-casting of zinc is a quick and dependable procedure that can be used to create high precision components that have complex shapes, tight tolerances, and high surface finishes. Strict design policies, including keeping wall thickness constant, incorporating draft, including ribs and fillets, and maximizing corner radius and maximum bosses, will make parts strong, durable and without defects. Surface finishes and ejection it is also well planned, which enhances functionality and minimizes post-processing requirements.

The cooperation with a professional and experienced manufacturer increases these advantages. The GC Precision Mold focuses on the manufacturing of high quality, precision zinc die-cast parts to a large number of industries. Our team offers design through to production services with high quality and consistency of parts that are strictly designed per specifications. Based on the idea of precision, reliability and customer satisfaction, GC Precision Mold can provide his components which will not only work perfect, but will also ensure your business success in an efficient and confident way.

Întrebări frecvente

What is zinc die-casting?

Zinc die-casting is used in the production of specific and elaborate parts by pouring the molten zinc into a mold.

So what is the significance of design guidelines?

They assist in avoiding defects such as, shrinkage or warping, and ensuring that the parts are strong and correct.

What are the available surface finishes to zinc parts?

Some of the most common finishes are the polishing, plating, painting, powder coating and texturing.

Is it possible to use zinc die- cast parts with threads?

Yes, however, with fine or small threads, threaded inserts are more convenient to increase the strength.

Why choose GC Precision Mold?

GC Precision Mold offers high quality, good, and accurate parts at a professional level and good customer service.