Die Casting Surface Finish: The Definitive FAQ Guide

Die casting surface finish is a process designed for altering the surface of a casted metal part by adding, removing, or reshaping.

It is often the final step in the manufacturing process of various die casted parts.

This process is quite essential in part production.

In this guide, we want to look at various elements surrounding die casting surface finish, such as the types, quality, cost, application techniques, etc.

Ideally, it is important because it makes it possible for you to attain the essential knowledge and make an informed decision regarding this process.

What Are The Main Preparation Methods For Die Casting Surface Finish Treatment?

Essentially, die casting parts often have a pattern of characteristic scratches on the workpiece caused by a wide range of elements.

Before treating such parts, it is always ideal for preparing the surface for better and effective compound adhesion.

The commonly used techniques include the following;

Die cast parts

Sanding

This process involves rubbing abrasive particles against workpiece’s surface to create a random, non-linear surface texture.

You can use various abrasive media with different grit depending on the type of surface finish required.

Rumbling And Tumbling

These two are more or less similar to sanding since they also use abrasive media to prepare the surface material.

However, rumbling and tumbling use loose sanding particles that are not necessarily fixed on a specific backing paper.

Some media you can use in this process include stones, coarse sand, walnut shells, garnet, etc., depending on a workpiece and desired finish.

Magnetic Polishing

It is an ideal surface preparation technique for complex parts with relatively difficult-to-reach surfaces.

Essentially, this method involves putting metal parts into a box filled with magnetized particles.

Thus, such particles are redirected to abrade away against interior surface attaining fine polish using a focused magnetic field.

Lapping

This is a precision technique for attaining highest surface refinement and flatness degree.

It involves using a soft iron tool with mild abrasive slurry to gradually work the surface using random, light, non-linear motions by hand.

In the end, it fills microscopic surface voids and flattens the high spots.

Grinding

This refers to a machining process used for removing irregularities on casting surfaces.

It provides a smooth surface, often done using a hand-held device known as a grinder or grinding wheel.

Essentially, grinding creates an ideal surface suitable for a wide range of finish coatings.

Filing

Filing involves using a file tool to aggressively remove unwanted material and shape metal relatively fast.

However, it often creates a somewhat rough and imprecise surface, which may require further polishing or sanding for better results.

Sandblasting

It is a surface treatment, which entails blasting the surface material by with abrasive media under high pressure.

Often, the specific type of media used determines the quality of resulting surface finish.

What Are The Typical Finishing Classes Of Die Casting Services?

Generally, your cast finishing requirements are likely to fall into one of the following classes

Utility Grade

It is a suitable surface finish for non-customer-facing die casting parts.

Often, this surface coating class hardly requires cosmetic finishes and has a low concern regarding surface imperfections.

Besides, utility-grade class is generally used as cast buy may need some protective coating.

Functional Grade

This die casting surface finish may feature decorative coatings.

Moreover, imperfections on the surface material of the part are spot-polished or painted over.

Commercial Grade

Typically, this surface finish class for die-cast parts is often used mostly in structural applications or parts used in high-stress projects.

It exhibits slight surface imperfections but provides reasonable means of removal.

Furthermore, commercial-grade casts are typically ideal for high-stress structural components.

Consumer Grade

It presents a high-class decorative coating with hardly noticeable surface imperfections.

Generally, the end goal of consumer grade coating is to produce special decorative parts.

Superior Grade

This die casting finishing class entails applying an alloy-dependent surface coating to limited areas of casting.

It has maximum value in micro-inches and is suitable for relatively small parts such as gaskets and O-ring seals.

What Are The Main Die Casting Surface Finishes?

Technically, die casting surface finishes are quite several, and often more are invented daily.

However, some of the popular finishes used in numerous cast parts include the following;

Anodizing

It is a non-conductive coating sealing the part.

You can find it in different colors but majorly blue, red and black.

It is quite an affordable option for creating corrosion resistance and durability.

Powder Coat

Quite a common surface finish is attained by curing the part under high temperatures to give it a tougher finish.

This finish is generally ding and scratch-resistant.

Furthermore, you can find it in various colors, textures, and gloss levels.

Chrome Platted

It is a surface finish that provides a mirror-like finish and is relatively costly since it involves immense labor quantity.

Mostly, it is used in automotive industry and other parts designed for exterior surfaces.

E-coating

This die casting surface finish is applied electrically to provide better and strong coverage on the part material.

You can use it as an undercoat for other coating processes, such as powder coating.

Ideally, e-coating is more functional than decorative.

Cobalt Tin

It is a relatively economical racked die casting surface casting process that resembles a chrome finish.

This surface finish exhibits immense corrosion resistance and wears properties.

Painting

Quite a popular and cost-effective surface treatment for die cast parts.

It involves painting casting and allowing it to dry to provide aesthetics to the part.

How Do You Choose The Right Die Casting Surface Finish?

Notably, the most appropriate die casting surface finish for your needs is dependent on the intended application.

Nonetheless, here are the main factors to guide you on how to obtain the suitable finish;

Metal Hardness

It is a fundamental element, especially when you are using processes in the second category.

Ordinarily, the more complex the die-cast metal, the more intense abrasive you will require.

However, it is advisable to avoid using softer metals because it could easily lead to part damages, which may be difficult to repair.

Production Speed

The time needed for delivering the finished parts is essential in determining the right die cast surface finish to consider.

It is necessary to compare the processing times of every metal finishing option at your disposal.

Cost And Budget

Ideally, different surface finishing for die casting parts vary depending on the specific application.

Even so, some tend to be quite expensive since they are complex and require expensive tools and equipment.

Thus, ensure the decision you make regarding ideal option is ideal and within your budget.

What Are The Common Defects Of Die Casting Surface Finish?

Powder coating surface defect

Die casting surface finish defects are quite a number and often caused by several factors.

Some occur due to complex metallurgical, physical, and chemical reactions, which the casting parts often go through during processing operations.

Such casting surface treatment imperfections include the following;

• Grain boundaries – It is a surface finish imperfection where crystalline structure or atomic arrangement is different from the adjoining grain.

Ideally, at specific spots in the grain boundary, the atoms are quite close, causing a region of compression.

• Stacking faults – Usually takes place in the face-centered cubic castings and represent an error in the stacking series of close-knitted planes.

This fault is common in interfering with slip process.

• Cissing – It refers to visible surface finish defect, which occurs due to inadequate or improper coating material application on casting parts.

Often, it is characterized by surface breakage of wet layer resulting in exposure of base material substrate.

• External surfaces – Ordinarily, it is the exterior dimensions of a material that exhibit surfaces where lattice ends abruptly.

Besides, exterior surface may be coarse or contain tiny notches, thus more reactive than bulk of material.

• Twin boundaries – This is a special grain boundary where there is a particular mirror lattice symmetry.

It interferes with slip process and increases strength of a metal.

What Is The Cost Of Applying Die Casting Surface Finish?

Different factors influence the actual cost of applying surface finish in die casting parts.

Some of these elements include the following;

Type Of Surface Finish

Notably, die casting surface finishes are quite several, and the ideal one usually varies based on the application needs.

As such, different casting surface finishes vary depending on the quality, quantity, technology, and labor requirements.

Some are a bit economical, whereas others tend to be quite costly.

Type Of Casting Material

Die casting materials are in plenty, including iron, steel, aluminum, and magnesium among others.

However, each material would yield better results when coated using different surface treatment techniques and types.

Therefore, you need to examine the specifications of the actual material to determine the most suitable coating finish and ultimately establish the cost.

Method Of Applying Surface Treatment

Ordinarily, you can use a wide range of techniques to apply surface treatment on casting surfaces.

It determines the actual cost of this process since some methods are a bit abrasive and demanding than others.

Manufacturer

Often, every manufacturer performing die casting surface coating charges different rates for their respective services.

Hence, you need to inquire diligently from your preferred manufacturer to establish the cost of their surface coating services.

What Are The Basic Features Of Die Casting Surface Finish?

Primarily, casting surfaces are relatively complex in character since each material exhibits a wide range of features.

Such features affect efficiency and function of a particular part in various ways.

Here are the notable casting surface finish characteristics;

• Texture – It refers to arrangement of random or repetitive deviations from the nominal surface forming its dimensional topography.
• Roughness – This refers to variation degrees from a smooth, nominal surface.

Ordinarily, this characteristic comprises inconsistencies in surface texture inherent to production method of casting part.

• Waviness – It refers to a surface texture component with superimposed roughness. Waviness can be a result of machine vibrations, deflections, warping of heat treatment among others.
• Lay – This refers to the predominant surface pattern direction often determined by production technique used.

How Do You Improve Good Die Casting Surface Finish Quality?

You can use various precision machining techniques, which include the following;

Precision Grinding

This method uses abrasives that are firmly attached to a rigid backing like a wheel.

Often, it is used before polishing to eliminate various surface imperfections and usually comes first in a typical finishing sequence.

Honing

It is a method, which uses silicon carbide or aluminum oxide abrasives.

This machining technique corrects spirals or tapers produced by the previous machining method.

Honing yields a characteristic crosshatched finish, which enhances the sealing ability of the material.

Polishing

This surface improving technique uses abrasives attached to a flexible backing firmly like a belt or wheel.

Ideally, this process is often used for maintaining close tolerances while enhancing the surface finish.

Buffing

It uses relatively fine abrasives often suspended in a lubricating binder to smoothen and brighten the casting surface finish.

Super-finishing

This is an abrasion process for refining the external diameter of various die casting cylindrical parts.

Why Is Die Casting Surface Finish Important?

Die casting surface finish presents quite a lot of advantages to the processed part.

Technically, an ideal surface finish ensures the final product is attractive and lasts longer.

Therefore, the end-user is the greatest beneficiary of die casting surface finish.

Among the several benefits of this process, here are some of the notable ones to have in mind;

• Enhances aesthetics

Die casting surface finish improves the overall appearance of a part, which is essential in enhancing its value and attracting end-users.

• Improves corrosion resistance

Often, corrosion is common destroyer of various metal parts and surfaces.

However, a correctly done surface finish protects the metal surface and allows it to last longer.

• Eases manufacturing process

An ideal surface coating makes it easy to manufacture different parts.

For instance, a properly brushed metal surface adheres to the paint quite easily, which is vital since it relieves the manufacturer.

• Increases strength and resistance to wear

Often, surface coating on die-cast parts enhances the overall strength.

In many instances, a properly coated surface will last for many years due to the added strength additives of the coating compound.

• Removes impurities and imperfections

This process creates an even surface, which is ideal, especially in eliminating manufacturing defects and impurities from the part’s surface.

• Prepare castings for subsequent treatment

Some surface coatings are essential in making the castings suitable for further processes.

In essence, it enables the part to conform to a different condition for effective subsequent surface treatments.

What Is Ra In Die Casting Surface Finish?

Die cast component

Usually, a smooth surface makes it quite difficult for the part to stick to the sides.

An ideal way to compare surface finishes is often by looking at surface roughness.

In essence, roughness often represents the casting surface smoothness.

However, smoother surface finishing is not necessarily advantageous as it may seem to be.

Thus, Ra is the most suitable parameter used for determining the surface roughness of casting material.

Primarily, Ra indicates the arithmetical deviation on the surface material.

Essentially, a small Ra number indicates a smoother surface, whereas a bigger Ra number shows a relatively coarse surface.

What Is The Difference Between Die Casting Surface Finish And Die Casting Surface Roughness?

Technically, die casting surface finish is mainly used for describing appearance of the casting part, which in most cases can be highly subjective.

In other words, you can hardly measure die casting surface finish

On the other hand, die casting surface roughness is objectively determined using calibrated equipment.

Thus, it means the value of casting surface roughness can indicate surface level finish indirectly.

Another difference is that casting surface finish can be expressed quantitatively using the attribute.

For instance, you may determine whether the turned surface is rough or tender.

On the other hand, you can only express casting surface roughness qualitatively.

Also, surface roughness provides several formulas for estimating the roughness of a machined casting surface.

On the contrary, there is hardly any formula you can use to estimate casting surface finish directly.

Besides, casting surface roughness has an absolute value, usually independent of human perception or requirement.

But die casting surface finish is merely expressed using attributes depending on requirement and human perception.

Why Is Surface Preparation Necessary Before Applying Die Casting Surface Finish?

Notably, surface preparation is a crucial initial phase in die casting surface finish.

It is important since it can save time, money and significantly reduce chances of surface coating failure.

Here are some of the reasons, which make surface preparation critical aspects before applying die casting surface finish;

Allows You To Identify Imperfections

You can find imperfections in the substrate in different shapes and sizes.

Thus, surface preparation makes it easy to remove such imperfections and makes die casting surface finish application efficient.

Prevents Bond Failure

The Foundation of any die casting surface coating system substantially depends on the surface preparation.

Ideally, the essence of surface preparation in die casting parts is to create a profile, which promotes mechanical adhesion by eliminating contaminants.

Chrome plated die cast part

How Do You Measure Die Casting Surface?

Measuring die casting surface entails establishing its surface roughness.

Thus, you need to correctly evaluate and analyze various irregularities you find on the surface.

Primarily, you can use these main ways to assess and analyze casting irregularities;

• Surface roughness comparator- It is a manual process that uses a roughness comparator hence demonstrates relatively low accuracy.
• Surface profile scanner – This method is more accurate and uses laser scanning.
• Coordinate measuring device – It is a machine with sensors fitted to automatically measure casting surface finishes.

Does Die Casting Surface Finish Control Flatness?

Not necessarily.

What happens is that flatness is regarded as macro-level measurement, whereas casting surface finish is micro-level measurement.

Ideally, flatness often has a relatively large impact on function and fit.

On the other hand, die casting surface finish is relatively more functional than fit.

What Are The Main Types Of Chemicals Used In Die Casting Surface Finish?

Primarily, die casting surface finishing uses a wide range of chemical substances, especially those used in electroplating process.

The commonly used chemicals include the following;

• Hydrochloric acid
• Ammonia
• Chromic acid
• Nitric acid
• Sodium Hydroxide
• Sulfuric acid
• Phosphoric acid

How Durable Is Die Casting Surface Finish?

Generally, a typical die casting surface finish is quite durable and can last for many years without wearing out or deteriorating.

However, the exact longevity of this component is dependent on various factors such as the following;

Type Of Surface Finish

Technically, different types of surface finishing have varied properties.

It means they exhibit different features such as resistance to corrosion and environmental factors, which determine the durability of the coating.

Application

Various casting parts with surface finish are used in different projects.

However, each project or application is subjected to different environmental conditions.

Therefore the exact conditions will determine the actual longevity of the specific surface finish.

Type Of Metal Surface

Ordinarily, some metals have better retention of surface finish than others.

Of course, the retention ability varies based on the properties of the metal and coating substrate.

As such, it is imperative to understand the properties of a specific metal surface to determine the idea die casting surface finish that would last accordingly.

Quality Of Casting Surface Finish

The craft involved in applying die casting surface finish determines its exact longevity.

Often, a substandard work would have a shorter lifespan than a superiorly applied surface finish.

Die cast components

Can You Redo Die Casting Surface Finish?

Yes.

However, it depends on the specific application of the casting part.

Some parts only take surface finish once after manufacturing due to the nature of the application where they are used.

In such instances, it would be relatively tricky to redo the die casting surface finish.

However, in other instances, you can redo this surface finish, but you have to prepare the surface finish appropriately to enhance proper adhesion.

What Are The Shortcomings Of Die Casting Surface Finish?

The major disadvantage of die casting surface finish is that it can be quite expensive depending on the specific type you choose.

Therefore, it is only economical when producing bulk casting parts.

For all your metal die casting process, contact us now.