Zinc Alloy Die Casting Process for Custom Metal Promotional Gifts

This is the core manufacturing process we use for the majority of our metal promotional products — including custom lapel pins, challenge coins, badges, keychains, medals and bottle openers. The same zinc alloy die-casting, plating and coloring workflow applies across these categories.We run our own zinc alloy die casting line. We are not a trading company that subcontracts your order. Design, mold making, die casting, plating, colour filling, assembly and packing all happen inside one factory site in Huizhou, so you never have to manage three suppliers for a single order.

The forming stage is identical across these categories. What differs is size, thickness and the surface finishing that follows, so the process below applies to a bookmark or a golf divot tool exactly as it does to a challenge coin. The 11 stages are listed in the order your order actually moves through them. For each stage you get the equipment, the parameters and, most importantly, what that stage decides for the finished product.

Verified factory with ISO 9001:2015 certification
SMETA and amfori BSCI audited production lines
11 in-house production stages, design to packing
100% inspection before shipment

What Happens to Your Order, Stage by Stage

Eleven stages stand between an approved artwork and a closed carton. The table gives you the full picture first, and each stage is broken out below. Read the last column carefully. Most quality failures are not a missing stage, but a stage that was done thin.

Stage	Process	Key Equipment / Materials	What It Determines
1	Design	PS, AI, CDR	Whether the artwork can hold a mold, and whether detail survives
2	Mold Making	Beijing JDPaint, CNC engraving machine, EDM machine, heat treatment furnace	Relief depth, edge sharpness, mold life
3	Die Casting	88-ton and 25-ton hot chamber machines, Zamak 3	Density, porosity, gate marks
4	Polishing	Wet integrated grinder, taro wheel, abrasive belt, hemp wheel, nylon wheel, polish wax	Edge feel, adhesion of the plating layer
5	Riveting	Bench drill, butterfly clutch, screw post, safety pin, simple pin	Accessory retention, clutch life
6	Surface Finishing	Plating tank, electrophoresis tank, spray gun and water curtain booth	Colour, gloss, oxidation and wear resistance
7	Colour Filling	Pantone card, rotary vane vacuum pump, MST-V4P automatic colouring machine	Colour deviation, bleed boundary, depth of the fill
8	Printing	UV flatbed printer, pad printer, vacuum screen printing machine	Graduated colour and photographic detail
9	Laser Marking	Laser marking machine	Engraving sharpness and permanence
10	Assembly	Ultrasonic welder, magnets, clasps, ribbons	Structural completeness and function
11	Packing	PP bag, blister box, velvet pouch, paper box	Transit damage and unboxing

Stage 1 to 2: Design and Mold Making

Half the quality of a finished metal part is decided before the mold is cut. A line drawn below 0.2mm on the artwork forces every later stage to compromise.

Artwork and Production Drawing

Our production drawings are made in PS, AI and CDR. That file is not just a pretty picture. It carries dimensions, colour numbers, the split positions of functional parts and any special process notes. If your source is a bitmap, a photograph or a rough idea, we redraw it into a vector file that can hold a mold. The detailed manufacturability rules (minimum line width, minimum fill space, minimum hole) live on our Custom Artwork Service page, so they are not repeated here.

Mold Design and 3D Drawing

Mold-3D-Design-Software — 3D Mold Design

After the production drawing is confirmed we build the 3D mold drawing in Beijing JDPaint, so the shape can be viewed from multiple angles. This step exists because a flat drawing hides problems: relief edges that collapse, side undercuts and lettering that fills in are all obvious in 3D. You approve the 3D drawing, not the flat file, which cuts rework after the mold is cut.

Mold Engraving and Fitting

Engraving turns the 3D drawing into the physical shape on the mold insert, cut on a CNC engraving machine along X, Y and Z axes. Two steps follow that most people never hear about.

Sub-process	Equipment	What it does	Why it matters
Spark erosion (EDM)	EDM machine	Leaves spark texture in local areas. Discharge grades run 1 to 7, with 3 and 5 used most	Texture is cut into the mold and finished before plating, so a matte finish costs nothing extra
Mold fitting	Milling machine, bench drill, bench tapping machine	Cuts the runner, gate and waterway positions, plus drilling, tapping and ejector pin fitting	Gate and waterway design decides whether zinc fills the cavity completely and whether porosity forms
Heat treatment	Heat treatment furnace	Spheroidised annealing, stabilising, quenching and tempering	Sets mold hardness, wear resistance and life. A well kept mold runs repeat orders for years

The mold base is selected, the insert fitted, and the whole assembly is test shot on the die casting machine. The mold is finished only when filling is complete, ejection is clean and there is no flash.

Tips: Mold cost and ownership follow the usual trade terms. We keep your mold for three years and refund the mold fee once the order reaches 10,000 pieces. Reorders go straight back onto the existing mold at no extra tooling charge.

Stage 3: Die Casting

Die casting is the stage where liquid metal is forced into the mold cavity under pressure and solidifies into the part. It sets the skeleton of the product, and every later surface treatment sits on that casting.

Shot Casting on 88-Ton and 25-Ton Machines

The zinc alloy is heated to a liquid state, and the molten metal runs down the channel and fills the cavity from the injection nozzle, solidifying under pressure. We run both 88-ton and 25-ton hot chamber machines: the large machines handle thick parts, large faces and multi-cavity tools, the small machines handle thin parts, small items and sampling. The split is not cosmetic. Shooting samples on a large machine wastes alloy and inflates the mold amortisation on your quote.

Deflashing and Trimming

After casting, operators on the floor separate each part from its gate by hand. Difficult gates come away with pliers, burrs are taken off with a wire brush, and holes that the polishing machine cannot reach are hand filed. Every step here is manual, and this is the most underestimated stage in the whole line. Gate residue left before polishing turns into a bright spot after plating, and you scrap the whole batch to fix it.

Why Zinc Alloy

ZnAl4 alloys 3, 5 and 7 are the standard grades, and we run grade 3 (Zamak 3) as the default. The reasons are practical: it casts well and produces clean surfaces on complex shapes, its fluidity fills fine teeth and dense texture, it accepts plating, electrophoresis and spray painting directly, and it melts at 385°C, which gives a wide casting window without cold shuts.

Material	Density	Main forming method	How we use it
Zinc alloy Zamak 3	6.7 g/cm³	Die casting	Main metal for badges, coins, keychains and bottle openers with relief
Brass	8.9 g/cm³	Stamping + cutting	Higher density and less porosity, for flat and thick-gauge parts
Iron	7.8 g/cm³	Stamping + cutting	Cheaper than brass but prone to rust, needs a protective plating layer
Aluminum	2.7 g/cm³	Stamping + anodizing	Light, suited to large thin flat parts

Stage 4 to 5: Polishing and Riveting

Polishing is the last rough stage before plating, and the first thing that protects your plating yield. Burrs and flow marks are exactly where plating builds up thick or breaks through.

Riveting Accessories

Backs, safety pins and screw posts are riveted onto the body after casting, with a bench drill pressing the accessory base into the zinc alloy joint. Three families cover most jobs: butterfly clutches and screw posts for badge backs, safety pins and simple pins for brooches, and misc riveted fittings. The metal thickness at the riveting point sets how strong the accessory holds. This is why some backs come out thinner than the standard. It is not a cost cut, the structure does not allow a thicker back.

Edge and Face Polishing

Splitting into edge polishing and face polishing, both on the wet integrated grinding machine. Edge work takes off the parting line and edge burr so the part is safe to handle; face work removes flow marks and shallow scratches and raises the quality of everything that follows. The wheel is chosen by the depth of the relief.

Polishing Consumables	Hardness	Suited to
Taro wheel	Soft, medium or hard	Soft for high relief, medium for low relief with lettering, hard for flat fronts and polished backs
Abrasive belt	Harder	Flattening flat faces and edge gates
Nylon wheel	Medium	General grinding
Hemp wheel	Standard	Hardware, stainless steel, aluminium, plated parts
Polish wax	Auxiliary	Speeds up polishing and leaves the surface smooth

Stage 6: Surface Finishing

Surface finishing decides what a part looks like it is worth. The same casting in shiny gold and in antique tin reads as two different price points. Below we open up all three finishing routes, because this stage is the biggest single variable in both your cost and the life of the product.

The alkaline copper plus acid copper structure deserves its own note. Alkaline copper solves adhesion. Acid copper solves brightness. A plant that runs a single layer looks fine in the first week and then blisters in damp service or under constant wear. The other detail people skip is wax removal: polish wax left on the surface makes the plating lift around each wax dot, which is why the pre-plating ultrasonic bath is heated to boiling.

The colour list is long, but grouped by nickel content and gloss: nickel-free true gold, light gold, dark gold, light and dark imitation gold, nickel-free gunmetal, standard white steel, wear-resistant thick white steel, nickel-free thick white steel, rose gold, 18K gold, 22K gold, heavy gold, black nickel, antique tin, antique silver, antique copper, antique bronze, antique gold, antique nickel, bright nickel, thick nickel, mist nickel, mist silver, mist gold and mist imitation gold. For skin-contact products such as badges, dog tags and keychains we suggest you specify a nickel-free tone.

Plating: Thirteen Stations and Two Copper Layers

Plating is not one step. It is a 13-station line.

Station	Step	Equipment / material	Function
1	Wax and oil removal	Ultrasonic cleaner heated to boil	Strips polish wax left from polishing
2	Hanging	Jigs	Conducts current, supports and locates the parts
3	Ultrasonic cleaning	Ultrasonic cleaner	Removes dust and dirt
4	Rinsing	Five clean water tanks in sequence	Washes off residue from the ultrasonic tank
5	Alkaline copper strike	Alkaline copper tank	Lays a base layer so the colour that follows grips and does not flake
6	Rinsing	Clean water tank	Washes off alkaline copper solution
7	Acid copper brightening	Acid copper tank, 20-60 min	Raises surface brightness and gloss. Longest step in the line
8	Rinsing	Clean water tank	Washes off acid copper solution
9	Electrolytic colouring	Plating tank: nickel, black nickel, pearl nickel, white K, bronze, imitation gold, antique tones	Produces the final colour
10	Rinsing	Clean water tank	Washes off excess plating solution
11	Drying	Tunnel oven, 100°C / 40 min	Hot air circulating drying
12	Oil spraying	Electrostatic spray gun: matte, semi-matte or gloss lacquer	Adds gloss and oxidation resistance and seals the plating
13	Unhanging	—	Parts must be fully cooled and colour fully cured before removal. Packed fresh from the oven, the colour is not set and sticks to the box

Electrophoresis: Antique Colours Without a Metal Plate

Electrophoresis deposits a paint film rather than a metal layer. Charged paint ions move to the cathode under voltage and react with the alkaline surface there to form an insoluble deposit that settles on the part. Its main advantage is coverage: hidden areas and deep recesses get a complete paint film, which spray painting cannot match.

The route runs deoiling (to strip release agent from casting), blackening (building an oxide film that gives antique contrast after sweeping), centrifugal drying, edge polishing, face polishing (a taro wheel removes excess black from front and back and lays in a brushed texture), hanging, ultrasonic cleaning, six clean water tanks in sequence, electrophoresis colouring, rinsing, tunnel oven drying, and unhanging.

Two details matter. First, the antique contrast comes from blackening and then sweeping the black off the raised surfaces, so recesses read darker. That is a property of the process, not a defect. Second, the hanging method is chosen by product: jigs run as hook hang, pocket hang and clip hang. Badges normally take clip hang, medals take hook hang, and the wrong choice leaves contact marks on the face.

Common electrophoresis colours: antique gold, antique brass, antique copper, antique sliver, matte black and black Nickel.

Spray Painting: Pantone Colours on Any Shade

Dimension	Plating	Electrophoresis	Spray Painting
Surface layer	Metal: copper, nickel, gold, silver	Pigment and resin particles from the bath	Atomised epoxy resin paint
Gloss	Metallic, matte available	Paint gloss with strong antique contrast	No metallic gloss, flat colour
Coverage	Strong, but watch deep recesses	Strongest, hidden areas fully covered	Weaker than electrophoresis
Precision	Set by the mold	Set by the mold	Set by the spray gun and tray layout
Cost	Highest	Lowest	Middle
Typical use	Gold, silver, rose gold and standard metallics	Antique tin, antique bronze, matte and gloss black	Customer-specified Pantone shades
Sequence	Polish, plate, then fill colour	Polish then electrophoresis (fill and coat normally combine)	Deoil, spray, cure

Stage 7: Colour Filling

Colour filling puts colour into the recesses of the metal, and it is the stage your artwork depends on most. Colour deviation and bleed boundaries are both decided here, so the parameters below are given in full.

Filling Methods and What They Look Like

Color Filling Options	English	Flow	Sequence	Result
Soft enamel, solid or translucent	Soft Enamel	Thin, flows well	Plate first, fill second	Clear raised metal edges with a slight dip in the colour
Imitation hard enamel	Imitation Hard Enamel	Thick	Fill, polish, then plate (reverse order)	A rotary tumbler brings metal level with the colour. No dip. Fuller colour
Solid glass enamel	Glass Enamel / Stain Glass	Thick, flows less than soft enamel	Plate first, fill second	Glass shine, brighter than soft enamel
Translucent glass enamel	Translucent Enamel / Stain Glass	Same as above	Plate first, fill second	See-through effect
Glitter	Glitter	Applied on top of soft enamel	Scattered evenly while the enamel is half dry during plate wiping, then AP film if needed	PET polyester film cut to uniform flakes, iridescent or single colour
Glow in the dark	Glow In The Dark	Powder or liquid	Liquid is applied after the enamel fully cures	Stores light releases a green glow in the dark. The effect always leans green

Matching Pantone Colours and Removing Air

The master mixer works to the Pantone card, dosing pigment and thinner (thinner adjusts viscosity), then filters the mix. A rotary vane vacuum pump, model 2XZ-8B, then pulls the air out of the paint. That step is the whole defence against bubbles: air that has not risen comes out as pinholes in the cured fill.

pantone-color-specifications-custom-pins

Soft Enamel Vs Imitation Hard Enamel

Soft enamel and imitation hard enamel differ in the direction of the sequence, and that direction sets the finished look. Soft enamel is plated and then filled: colour stays in the recess, metal edges stand proud, and the part has relief under your finger. Imitation hard enamel is filled, polished and then plated: metal and colour finish on the same plane, the surface is flat to the touch, colour is fuller, and both price and lead time run higher. Which one you want changes both the quote and the schedule.

Filling, Baking and Wiping

Two routes fill the part. One is the MST-V4P automatic colouring machine: a high-definition camera shoots a 360-degree panorama to auto-position the part, the software detects and skips already-coated areas, and it suits complex parts and large volumes. The other is a manual syringe for the corners the machine cannot reach.

Filled parts go into the oven in two stages.

Stage	Temperature	Time	Purpose
Low temperature baking	60-70°C	60-90 min	Bakes to half dry only, so the next step can wipe
Plate wiping	—	—	A cloth wrapped over a flat metal face with alcohol lifts excess paint off the lines
Final drying	100°C	60 min	Cures the paint completely

Automatic-Color-filling-Process
Industrial-Oven
Manual-Coloring-Process

Plate wiping decides the fill quality. Wax or paint left on a line blurs the edge of a logo and closes fine lettering, and after that all the mold and casting work is invisible. This is the step where a good shop separates itself.

Special Effects

Sandblasting can be sprayed directly or injected with a syringe. It reads flatter than spark texture, and it is applied before or after plating depending on the product. Glitter and glow powder both go on while the soft enamel is half dry. An AP protective layer is added where the product needs it, most often on printed or printed-and-cured pieces.

Stage 8 to 10: Printing, Laser and Assembly

Casting and colour filling give the part its body. Printing, laser and assembly decide whether it lands as your design. The printing methods are not interchangeable: picking the wrong one does not degrade the result slightly, it makes the artwork impossible to run.

Three Printing Methods

Method	Equipment	What it renders	Limitation
UV printing	UV flatbed printer	Flat and 3D surfaces, printed straight onto metal or over a paint layer, supports photographic detail and gradients. Relief must stay within 7mm	Beyond that limit focus loss costs sharpness
Pad printing	Pad printer	Image carried from an etched steel plate to the part by a silicone head, ink matched to the material	Not for large-area gradients
Screen printing	Vacuum screen printing machine	Spot colour printing, priced by colour count	No gradation
Offset printing	—	Flat parts, normally finished with an AP protective layer	Flat parts only

The 7mm relief limit on UV printing is worth flagging. If your artwork carries high relief or a large height difference across the face, UV sharpness drops and you should move to screen or pad printing, or split the raised face out as a separate stage.

Laser Marking

A laser marking machine puts a high-energy beam on the surface, converts light to heat in an instant and vaporises the surface to cut the text, shape or image. Its advantages are permanence and fineness. Fine lettering, serial numbers and QR codes hold better under laser than under printing.

Assembly: Clasps, Magnets and Ribbons

Assembly item	Common forms	Notes
Clasp	Swivel clutch, lobster clasp, split ring	Standard connections for medals
Magnet	Round and rectangular in 2, 3, 4, 5, 6, 8, 10, 12, 15mm	Bonded with yellow glue or AP glue
Bought parts	Movements, acrylic, electronic components	Fixed with glue or compressed by screw
Ribbon	Heat transfer, nylon, faux suede cord, bead chain, satin, wax cord	Pressed on by an ultrasonic plastic welder

Ribbons are welded by an ultrasonic plastic welder: high-frequency electrical energy becomes mechanical vibration, then friction heat, which melts the fabric together. The magnet list gets asked about often. Larger diameter gives more pull but takes more space on the back of the part, so small parts end up limiting the magnet size. That is a structural trade, not a downgrade.

Stage 11: Packing

Packing decides the condition your goods arrive in, not just how they look. The pack format has to be fixed before cartoning because it drives carton dimensions and freight.

Choose by product need or protection: PP bag, OPP self-adhesive bag, zip bag, velvet pouch, paper card, blister box, velvet box, acrylic box, paper box, tin and gift box. Functional parts, meaning anything with a butterfly clutch, a magnet or a hinged structure, get an individual polybag or blister so they cannot scratch or knock each other in transit. Cartons are palletised to export standard with a packing list attached.

Hinged and rotating structures must be packed individually. That is a hard rule on our quality control page, because these are the structures that break first in transit. Full inspection points, measurable acceptance criteria and the pre-shipment inspection standard live on quality control.

Choosing the Right Finish for Your Design

The combination of surface finishing and colour method sets the positioning, price and durability of the part. This table works backwards from your artwork, which is faster than reading every option in turn.

Your artwork	Recommended route	Result and typical use	Relative cost
Bold lines, few colour blocks, metal relief wanted	Plated gold or silver plus soft enamel	Classic badge feel, edges raised, colour slightly dipped	Baseline
Flat and full colour wanted	Plating plus imitation hard enamel	Metal and colour on one plane, fuller colour	Higher
Translucent and bright	Plating plus solid or translucent glass enamel	Glass shine, brighter than soft enamel	Above soft enamel
Photography, gradient, multi-colour illustration	UV printing	Prints straight on metal or paint, photographic quality	By complexity
One or two spot colours, large volume	Screen printing	Spot colours only, no gradient	Low
A specified Pantone shade	Spray painting	No metallic gloss, any colour	Medium
Aged, vintage, military and collector tone	Electrophoresis in antique tin or bronze with blackening and sweep	Recesses read dark, strong antique contrast, fullest coverage	Lowest
Maximum flatness	Plating then sandblasting	Flatter than spark texture, billed separately	Surcharge

Three combinations worth warning about:

First, soft enamel cannot carry very fine lines or dense texture. Below 0.2mm line width or under 0.3mm fill space, move to UV printing.
Second, imitation hard enamel runs the sequence in reverse, so its lead time is longer than soft enamel. Confirm this early on rush jobs.
Third, plating colour names must be written in full. Matt silver and silver are two different shades. We attach the shade card to the quote and the confirmation, and we give you the English colour name and a photo of the physical chip.

Zinc Alloy Die Casting FAQ

Eleven stages. Production drawing, mold making (3D drawing, engraving, fitting, heat treatment), die casting, polishing, riveting, surface finishing (plating, electrophoresis or spray painting), colour filling, printing, laser marking, assembly and packing. Every stage runs inside one factory site in Huizhou.

Zinc alloy grade 3 (Zamak 3) is our main metal, at 6.7 g/cm³ and a 385°C melting point, which suits three-dimensional metal parts and takes surface treatment well. Grades 5 and 7 are used by product need. Brass is stamped, iron and aluminium are stamped and cut, for flat parts and large thin sections.

100 pieces per design. Some categories shift slightly with mold and process differences, and your quote will confirm the figure.

Samples take 7-10 days and bulk orders take 15-18 days. Lead time starts from PI confirmation and pre-production sample approval. Rush jobs can be assessed against existing molds and shorter-cycle processes.

Decide on the finish you want to feel. Soft enamel is plated then filled: metal edges stand proud and the colour sits slightly low, which is the classic badge look. Imitation hard enamel is filled, polished then plated: metal and colour end on one plane, the surface is flat, the colour is fuller, and it costs more and takes longer. Artwork under 0.2mm line width or under 0.3mm fill space should move to UV printing.

Plating lays a metal layer with metallic gloss and the highest oxidation and wear resistance, at the highest cost. Electrophoresis deposits a paint film with the strongest coverage, so hidden areas are fully coated, strong antique contrast, at the lowest cost. Spray painting uses epoxy resin paint with no metallic gloss and can hit any Pantone colour at a middle cost. The full comparison sits in the table under Stage 6 above.

Yes. Paint is mixed to the Pantone card and the colour number is confirmed in writing at the pre-production sample stage, with the shade card attached to the quote and the confirmation. Plating colour names must be written in full: matt silver and silver are different shades. We give you the English colour name and a photo of the physical chip.

Yes, all internally. Beijing JDPaint produces the 3D drawing, a CNC engraving machine cuts the insert, an EDM machine lays the spark texture, a milling machine and bench drill cut the gate and waterway, and a heat treatment furnace treats the steel. We keep your mold for three years and refund the mold fee once the order reaches 10,000 pieces.

Yes. We hold SMETA and amfori BSCI social compliance audits and ISO 9001:2015 certification, and we support client factory visits and third-party audits. Certifications and audit reports are on certifications.

Colour number, plating colour and structure are confirmed in writing on the pre-production sample. If bulk goods deviate from the confirmed sample, the discrepancy is answered within 24 hours, we compare with photos and video, and affected batches are reworked, replaced or refunded under contract terms where the responsibility is ours.

Send Us Your Artwork and We Will Quote the Full Process

You have now seen all 11 stages. The next step is direct: send us your artwork, your sample or just the idea, and we will tell you how that design runs on our line, which processes it needs, how long sampling takes and what the bulk order costs. With complete information we return a detailed quote in as little as 12 hours.