1. Overview
Primary Shaping refers to a group of manufacturing processes that create the basic shape of a product or part directly from raw material. Materials such as metals, plastics, powders, ceramics, and rubber are prepared in liquid, molten, powder, viscous-flow, or formable states, and then shaped into the desired geometry using molds, dies, or forming cavities.
Primary Shaping does not create geometry by removing material like machining. Instead, it fills, compresses, solidifies, or cures material inside a defined cavity to produce the initial form of a part. For this reason, it can efficiently produce complex three-dimensional shapes and plays an important role in repeated production and mass production.
Representative Primary Shaping processes include the following.
Casting
Die casting
Injection molding
Compression molding
Blow molding
Powder forming
Ceramic forming
Rubber molding
Initial extrusion shaping
In mechanical design, Primary Shaping is not simply a process of “forming a shape with a mold.” It is a design-driven manufacturing process that requires consideration of mold structure, material flow, shrinkage rate, cooling conditions, wall thickness, draft angle, porosity, machining allowance, and production volume.
2. Role of Primary Shaping
The core role of Primary Shaping is to convert raw material into the basic shape of a part.
Material removal processes remove unnecessary portions from an existing workpiece. In contrast, Primary Shaping creates the material form close to the desired geometry from the beginning. Therefore, it can reduce material waste, produce complex shapes in a single process, and become more economical as production volume increases.
The role of Primary Shaping can be summarized as follows.
Creates the basic shape of a product from raw material.
Efficiently realizes complex three-dimensional geometry.
Reduces unit cost in repeated production.
Reduces the amount of machining required.
Secures shape repeatability through molds or dies.
Limits post-machining to only necessary areas.
Forms the basic manufacturing structure of mass-produced products.
For example, gearbox housings, pump casings, motor covers, plastic covers, handles, resin parts for food machinery, and rubber packing components are often produced by Primary Shaping first, followed by post-machining only where necessary.
3. Basic Principle of Primary Shaping
Primary Shaping is based on the principle that material fills a defined cavity and then solidifies, cures, or is compressed to obtain the basic shape of a part.
The basic process flow is as follows.
The material state differs depending on the process.
Material State | Applicable Process | Description |
|---|---|---|
Molten metal | Casting, die casting | Metal is melted and poured or injected into a mold |
Molten plastic | Injection molding | Plastic is melted and injected into a mold under high pressure |
Powder | Powder forming, sintering | Metal or ceramic powder is compacted and then sintered |
Rubber or viscous material | Rubber molding, compression molding | Viscoelastic material is compressed or vulcanized in a mold |
Molten or softened material | Extrusion, blow molding | Continuous cross-sections or hollow shapes are formed |
The common principles of Primary Shaping are as follows.
The material must sufficiently fill the mold or cavity.
Shrinkage occurs during cooling or curing.
The part must be removable from the mold.
Non-uniform wall thickness causes deformation and defects.
Precision functional surfaces may require post-machining.
The balance between mold cost and production volume must be considered.
4. Classification of Representative Processes
Primary Shaping can be divided into several processes according to material and shaping method.
Process | Applicable Materials | Main Characteristics |
|---|---|---|
Casting | Iron, aluminum, copper alloys, etc. | Suitable for large metal parts and complex shapes |
Die Casting | Aluminum, zinc, magnesium alloys | Suitable for high-speed repeated production and thin-wall shapes |
Injection Molding | Thermoplastics | Suitable for mass production of plastic parts |
Compression Molding | Thermosetting resins, rubber | Suitable for relatively simple and thick molded parts |
Blow Molding | Plastics | Suitable for hollow containers, ducts, and tanks |
Powder Forming | Metals, ceramics | Suitable for high-hardness, porous, or complex material compositions |
Rubber Molding | NBR, EPDM, silicone, etc. | Suitable for packing, seals, and vibration-isolation parts |
Ceramic Forming | Alumina, zirconia, etc. | Suitable for heat-resistant, wear-resistant, and insulating parts |
These processes all belong to Primary Shaping, but their design criteria are different. Cast parts require consideration of shrinkage and porosity, while injection-molded parts require consideration of resin flow and wall thickness. Powder-formed parts require consideration of compaction direction and sintering shrinkage, while rubber-molded parts require consideration of compression ratio and elastic recovery.
5. Casting
Casting is a process that creates part geometry by melting metal, pouring it into a mold, and allowing it to solidify. It is suitable for complex metal shapes, large parts, and structures with internal cavities.
Representative casting methods include the following.
Sand casting
Permanent mold casting
Investment casting
Centrifugal casting
Shell mold casting
Lost-wax casting
Die casting
The advantages of casting are as follows.
Complex shapes can be produced.
Large parts can be manufactured.
Internal cavities and rib structures can be formed.
Machining volume can be reduced.
Economic efficiency improves as production volume increases.
However, casting has the following limitations.
Shrinkage occurs.
Internal porosity or shrinkage cavities may occur.
Surface quality may be lower than machined surfaces.
Precision dimensions require post-machining.
Mold or pattern design is required.
Defect control can be difficult depending on material and geometry.
Designers should consider the following items.
Shrinkage rate
Casting draft
Uniform wall thickness
Fillets and rounded corners
Rib structure
Gate and riser location
Machining allowance
Reference surface after casting
Internal porosity inspection
Need for heat treatment
In cast part design, thick sections and thin sections should not be connected abruptly. Large differences in cooling rate can easily cause shrinkage defects. Sharp corners can also cause stress concentration and casting defects, so appropriate radii should be applied.
6. Die Casting
Die casting is a process in which molten metal is injected into a metal die under high pressure and rapidly solidified. It is widely used for mass production of aluminum, zinc, and magnesium alloy parts.
The advantages of die casting are as follows.
Production speed is high.
Thin-wall shapes can be produced.
Dimensional repeatability is good.
Surface quality is better than general casting.
Complex ribs, bosses, and mounting features can be formed.
The limitations of die casting are as follows.
Die cost is high.
There are limitations for very large parts.
Internal porosity may occur.
Heat treatment or welding may be limited.
Design changes are costly.
Designers should consider the following items.
Uniform wall thickness
Appropriate draft angle
Thickness of ribs and bosses
Gate location
Ejector pin location
Parting line
Machining allowance
Possibility of porosity
Thread and insert structure
Die cooling structure
Die-cast parts are suitable for motor housings, gearbox covers, electrical enclosures, brackets, handles, and cover parts. However, for parts requiring airtightness or welding, internal porosity must be carefully reviewed.
7. Injection Molding
Injection molding is a process in which plastic material is heated, melted, injected into a mold under high pressure, and then cooled and solidified. It is the most widely used Primary Shaping process for mass production of plastic parts.
The advantages of injection molding are as follows.
Mass productivity is very high.
Complex shapes can be repeatedly produced.
Part unit cost can be reduced.
Color, surface texture, and insert structures can be applied.
Parts can often be used without post-processing.
The limitations of injection molding are as follows.
Mold cost is high.
Design changes are difficult.
Shrinkage and warpage may occur.
Sink marks may occur in thick sections.
Mold release direction must be considered.
Undercut structures require slide cores.
Designers should consider the following items.
Uniform wall thickness
Resin flow direction
Gate location
Weld lines
Sink marks
Warpage
Draft angle
Rib thickness
Boss structure
Undercuts
Ejector pin marks
Shrinkage rate
Mold cooling
One of the most important design principles in injection molding is to maintain wall thickness as uniformly as possible. Large differences in thickness cause differences in cooling rate, which can lead to shrinkage, deformation, and sink marks.
Ribs are used to increase stiffness, but if ribs are too thick, sink marks may appear on the opposite surface. Bosses are used for screw fastening or insert placement, but they should be designed together with surrounding ribs and fillets to reduce cracking and deformation.
8. Powder Forming and Sintering
Powder forming is a process in which metal, ceramic, or composite powder is compacted inside a die to create a shape, and then sintered to bond the particles together.
Typical applications include the following.
Powder metallurgy parts
Ceramic parts
Sintered bearings
Filters
High-hardness parts
Magnetic material parts
Porous structure parts
The advantages of powder forming are as follows.
Material utilization is high.
Complex material compositions can be produced.
High-melting-point materials can be formed.
Porous structures can be created.
It is suitable for repeated production.
The limitations of powder forming are as follows.
There are restrictions related to compaction direction.
Density distribution may not be uniform.
Sintering shrinkage occurs.
There are limitations for large parts.
Additional processes may be required for high-strength parts.
Designers should consider the following items.
Compaction direction
Ejection direction from the die
Sintering shrinkage rate
Density distribution
Uniformity of thickness
Possibility of corner cracking
Need for post-machining
Porosity
Material composition
Sintering temperature
Powder-formed parts are advantageous for producing material compositions or porous structures that are difficult to make by ordinary machining. However, to secure strength and dimensional accuracy, additional processes such as sizing, coining, heat treatment, or impregnation may be required after sintering.
9. Rubber and Elastomer Molding
Rubber molding is a process in which rubber or elastomer material is compression-molded, injection-molded, or transfer-molded inside a mold, then vulcanized or cured under heat and pressure to form the final shape.
Representative materials include the following.
NBR
EPDM
Silicone
Viton
Urethane
Natural rubber
Typical components include the following.
Packing
O-rings
Seals
Vibration-isolation mounts
Rollers
Cushion parts
Silicone parts for food machinery
The advantages of rubber molding are as follows.
It is suitable for producing parts with elastic functions.
Sealing, vibration isolation, and cushioning functions can be realized.
Complex cross-sectional shapes can be produced.
Repeated production using molds is possible.
Design considerations for rubber molding include the following.
Compression ratio
Elastic recovery
Hardness
Vulcanization shrinkage
Parting line
Flash generation
Mold release
Heat resistance
Oil resistance
Chemical resistance
Food-contact suitability
For sealing parts, compression ratio and contact pressure are very important. Insufficient compression can cause leakage, while excessive compression can cause wear and assembly problems. In food machinery, food-contact suitable materials such as silicone and EPDM should be selected, and cleaning chemicals and temperature conditions must also be reviewed.
10. Design Criteria for Primary Shaping
The first thing a designer must consider in Primary Shaping is whether the geometry can be produced using a mold, die, or forming cavity.
The main design criteria are as follows.
10.1 Draft Angle
A draft angle is required to remove the part from the mold. If vertical walls are perfectly perpendicular, mold release becomes difficult, and surface damage or mold wear may occur.
10.2 Shrinkage Rate
Materials shrink during cooling or curing. Metals, plastics, rubber, and powder materials all have different shrinkage characteristics. Designers must consider the difference between final part dimensions and mold dimensions.
10.3 Uniform Wall Thickness
If wall thickness is non-uniform, differences in cooling rate can cause deformation, shrinkage defects, sink marks, and porosity. It is preferable to maintain uniform thickness as much as possible and replace thick sections with ribs or hollow structures.
10.4 Rounds and Fillets
Sharp corners disturb material flow and create stress concentration. In casting, injection molding, and powder forming, appropriate radii should be applied to improve material flow and strength.
10.5 Machining Allowance
Primary Shaping creates the basic shape of a part, so precision reference surfaces, bearing mounting areas, sealing surfaces, and locating surfaces may require post-machining. Therefore, machining allowance must be reflected during the design stage.
10.6 Parting Line and Gate
The mold parting line and material injection location affect appearance, strength, deformation, and post-processing. The parting line should avoid functional surfaces or visually important surfaces. Gate location should be determined by considering material flow and shrinkage direction.
11. Defects and Quality Issues
In Primary Shaping, various defects can occur during material flow, cooling, shrinkage, and mold release.
Representative defects include the following.
Defect | Main Processes | Cause |
|---|---|---|
Shrinkage cavity | Casting, die casting | Volume shrinkage during cooling |
Porosity | Casting, die casting | Gas entrapment or poor solidification |
Short shot | Injection molding, casting | Insufficient material filling |
Weld line | Injection molding | Meeting of resin flow fronts |
Sink mark | Injection molding | Shrinkage in thick sections |
Warpage | Injection molding, casting, rubber molding | Uneven cooling and residual stress |
Flash | Injection molding, rubber molding | Material leakage through mold gaps |
Cracking | Forming, sintering, casting | Stress concentration or uneven cooling |
Dimensional defect | All processes | Shrinkage rate, mold wear, process condition variation |
Designers should understand that these defects are not merely production-floor problems. They are directly related to design geometry. If wall thickness is non-uniform, draft is insufficient, gate location is inappropriate, or machining allowance is insufficient, the possibility of defects increases.
12. Primary Shaping and Post-Machining
Parts produced by Primary Shaping often do not become final products as-is. Functionally important areas require post-machining to secure precision and surface quality.
Representative post-processing items include the following.
Reference surface machining
Bearing bore machining
Tapping
Fastening surface machining
Sealing surface machining
Grinding
Deburring
Surface treatment
Cleaning
Inspection
For example, in a cast housing, the overall external shape is produced by casting, while the bearing mounting areas and bolt seating surfaces are finished by CNC machining. In a die-cast cover, the basic shape and rib structure are created by the die, while only threaded areas or precision mounting areas are post-machined.
In Primary Shaping design, the important question is not simply whether the final shape can be made in one process. The important decision is which areas should be shaped by the mold and which areas should be finished by post-machining.
13. Production Volume and Economic Feasibility
Primary Shaping often requires molds, dies, patterns, or dedicated equipment. Therefore, initial investment is high, but as production volume increases, the cost per part decreases.
The relationship between production volume and economic feasibility can be summarized as follows.
When selecting Primary Shaping, the following cost elements should be reviewed.
Mold manufacturing cost
Mold modification cost
Material cost
Cycle time
Defect rate
Post-machining cost
Surface treatment cost
Inspection cost
Possibility of design change
Expected production volume
In the early development stage, design changes are frequent, so proceeding directly to mold production can be risky. In such cases, it is preferable to verify prototypes using 3D printing, CNC machining, soft tooling, or silicone molds before moving to production molds.
14. Application of Primary Shaping in Food Machinery
In food machinery and meat-processing machinery, Primary Shaping is mainly applied to plastic parts, rubber seals, aluminum or stainless castings, handles, covers, and guide parts.
Representative applications include the following.
Food-grade plastic guides
UHMW-PE or POM molded parts
Silicone packing
Rubber seals
Aluminum die-cast covers
Plastic handles
Motor covers
Pump housings
Hygienic resin parts
When applying Primary Shaping to food machinery, the following should be considered.
Confirm that the material is suitable for food contact.
The shape should not allow contamination to remain on the surface.
Cleaning liquid should not be trapped.
Parting lines and flash should not remain on food-contact surfaces.
Rubber or plastic parts must withstand cleaning temperatures and chemicals.
Resin parts should be reviewed for wear-related foreign-material generation.
Color may be selected considering foreign-material detectability.
If metal detection is required, detectable materials may be considered.
For food-contact parts, it is not enough for the geometry to fit. Surface quality, cleanability, wear, material certification, and possible lubricant contact must also be reviewed.
15. Connection with Other Knowledge Tracks
Primary Shaping is closely connected with other Knowledge Tracks.
15.1 Connection with Material
Primary Shaping strongly depends on material flowability, shrinkage rate, cooling behavior, and thermal properties. Material selection directly determines moldability and quality.
15.2 Connection with Mechanism & Motion
In moving parts, Primary Shaping can be used to create the basic shape, but precision motion surfaces may require post-machining.
15.3 Connection with Assembly
Primary Shaping parts can include assembly references, fastening areas, and locating structures. Therefore, bosses, ribs, fastening surfaces, and insert structures should be designed with assembly in mind.
15.4 Connection with Manufacturing Quality
Primary Shaping is prone to quality issues such as shrinkage, porosity, warpage, flash, and incomplete filling. Therefore, process conditions and inspection criteria must be established together.
16. Core Thinking
The core thinking in Primary Shaping is as follows.
The part geometry must be removable from the mold or die.
Material shrinks during cooling or curing.
Non-uniform wall thickness creates deformation and defects.
Trying to mold every surface with high precision reduces the advantage of the process.
Precision functional surfaces are usually secured through post-machining.
Draft angles, radii, ribs, bosses, and gate locations determine quality.
Mold cost is an initial cost, but it reduces unit cost when production volume is high.
Mold-based processes should be applied carefully when design changes are expected.
Primary Shaping offers high geometric freedom, but it is constrained by mold structure and material flow.
Good Primary Shaping design considers moldability, post-machinability, assembly, and inspectability at the same time.
17. Conclusion
Primary Shaping is a group of manufacturing processes that create the basic shape of a part from raw material. Processes such as casting, die casting, injection molding, powder forming, and rubber molding can efficiently produce complex shapes and provide high economic efficiency in repeated production.
However, Primary Shaping is not simply a process of putting material into a mold to create a shape. Designers must consider shrinkage rate, draft angle, wall thickness, parting line, gate location, cooling conditions, machining allowance, defect risk, and production volume.
From the mechanical design perspective, the key points of Primary Shaping are as follows.
What material will be shaped, and in what state?
Can the geometry be made using a mold or die?
Are shrinkage and deformation after shaping acceptable?
Which precision functional surfaces should be post-machined?
Can the mold cost be recovered through production volume?
Can defects be inspected and controlled?
Is the structure suitable for assembly and maintenance?
Therefore, Primary Shaping is a key section in the Manufacturing Track for understanding basic shaping processes. It naturally connects to Material Removal, Surface Engineering, Finishing, and Assembly as part of a complete manufacturing knowledge system.