Blank Selection and Forming Methods in Mechanical Manufacturing

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In mechanical manufacturing, selecting and forming blanks are critical factors that influence product quality, cost, and performance. Choosing the right blank can improve production efficiency and significantly reduce manufacturing costs. This article will provide a detailed introduction to the principles of blank selection and the comparison of common forming methods.

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Principles of Blank Selection

Processability Principle

The processability principle for selecting blanks is based on the usage requirements of the parts to determine their shape characteristics. Different parts have different external and internal quality requirements, such as shape, size, machining accuracy, surface roughness, chemical composition, metal structure, mechanical properties, etc.

When selecting the blank forming method, the process characteristics of the part material must be considered. For example, gray cast iron parts should not use forging methods, and thin-walled blanks with poor fluidity should not use casting methods. It is also essential to consider the machinability of the blank for subsequent machining processes.

Adaptability Principle

The adaptability principle requires selecting blanks based on the structural shape, size, and working conditions of the parts. For example, stepped shaft parts with similar diameters can be manufactured using bar stock, while complex-shaped thin-walled blanks should avoid metal casting. Critical parts like spindles require high-quality materials and processing through forging and heat treatment, while simple parts like machine handles can be made from gray cast iron with minimal machining.

Principle of Production Conditions

The forming scheme for blanks should consider production conditions, including process level, equipment status, and the feasibility of outsourcing. If current conditions cannot meet the requirements, changing the material or forming method, or outsourcing the process, can be considered.

Economic Principle

The economic principle aims to select the lowest overall production cost scheme by comparing different forming methods. Generally, the blank’s size and shape should closely match the finished part to reduce machining allowances and workload.

Sustainability Principle

The sustainability principle emphasizes considering environmental protection and energy-saving issues during the blank selection and forming process. Choosing low-energy and environmentally friendly forming methods and materials can help achieve sustainable industrial development.

Comparison of Common Blank Forming Methods

Common blank forming methods include casting, forging, powder metallurgy, stamping, welding, plastic forming, ceramic forming, composite forming, and rapid prototyping.

Casting

Casting involves filling a mold with molten metal and allowing it to solidify, suitable for manufacturing various sizes and complex-shaped parts like housings, boxes, and machine beds. Manual sand casting is suitable for single-piece and small-batch production, while machine molding is used for mass production.

Forging

Forging is the process of shaping metal using compressive forces, suitable for making dense and strong parts like gears and crankshafts. Open die forging is used for single and large parts, while die forging is suitable for medium and large batch production.

Powder Metallurgy

Powder metallurgy involves forming and sintering metal powders to create parts, ideal for manufacturing small to medium-sized complex parts with special properties.

Stamping

Stamping uses dies to shape metal sheets, suitable for producing parts with complex shapes and high production rates, such as automotive panels and instrument boards.

Welding

Welding joins materials by heating or applying pressure, suitable for complex or large component assemblies and repairs.

Plastic Forming

Plastic forming methods include injection molding, extrusion, and compression molding, suitable for producing general structural and wear-resistant parts. Plastic forming is widely used due to its low cost and simplicity.

Ceramic Forming

Ceramic forming uses methods like slip casting and plastic forming, suitable for making high-hardness, high-temperature, and corrosion-resistant parts like tools and bearings.

Composite Forming

Composite materials are formed by combining matrix and reinforcing materials, offering high strength and stiffness, suitable for applications like ship hulls and car bodies.

Rapid Prototyping

Rapid prototyping involves creating 3D models by material accumulation, suitable for product design, prototype testing, and custom manufacturing.

Comparison of Material Forming Methods

Forming MethodForming CharacteristicsProcess RequirementsPart FeaturesMaterial UtilizationProduction RateMain Applications
CastingMolten metal fills moldGood fluidity, centralized shrinkageVarious, complexHighLow to highComplex cavity parts like housings, boxes, beds, etc.
Open Die ForgingPlastic deformation of solid metalLow deformation resistance, good plasticityVarious, simpleLowLowTransmission shafts, gear blanks, barrels, etc.
Die ForgingPlastic deformation of solid metalLow deformation resistance, good plasticitySmall to medium, complexHighHighHigh-stress, complex parts like gears, valves, etc.
StampingSeparation or deformation by diesGood plasticity, low deformation resistanceVarious, complexHighHighLightweight, rigid parts, complex shapes like covers, etc.
Powder MetallurgyAtomic diffusion, recrystallization of powdersGood powder flow, high compressibilitySmall to medium, complexHighHighPrecision parts or special properties like bearings, tools
WeldingJoint by metal pool solidification or deformationLow hardening, cracking, porosity tendencyVarious, complexHighLow to highComplex or large component assemblies, repairs, etc.
Plastic FormingInjection, extrusion, compression moldingGood fluidity, low shrinkage, low moisture sensitivityVarious, complexHighHighGeneral structural parts, wear-resistant components
Ceramic FormingForming by slip casting, plastic forming, etc.Uniform, dense body structureSmall to medium, complexHighLow to highHigh-hardness, high-temperature parts like tools, bearings
Composite FormingMatrix and reinforcing material combinationHigh fiber strength and stiffness, good plasticity of matrixVarious, complexHighLow to highHigh strength, stiffness parts like hulls, bodies, tanks
Rapid PrototypingMaterial accumulation forming 3D modelsSatisfy usage requirementsVarious, complexHighFastProduct design, prototype testing, custom manufacturing

Understanding the characteristics and applications of different blank forming methods can help in selecting the most suitable process, improving production efficiency, product quality, and reducing costs, while promoting sustainable development.

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