Chp 5 - Manufacturing Processes in Design

Transcription

1 ME 530 Designing for Production Chp 5 - Manufacturing Processes in Design Mechanical Engineering University of Gaziantep Dr. A. Tolga Bozdana Assistant Professor

2 Classification of Manufacturing Processes The common methods of material processing are as follows: 1. Solidification (casting) processes: molten metal, plastic or glass casting 2. Deformation processes: forging, rolling, extrusion, etc. 3. Material removal or cutting (machining) processes: turning, milling, drilling, etc. 4. Polymer processing: injection molding, thermoforming, etc. 5. Powder processing: sintering, compaction, and so on. 6. Joining processes: welding, soldering, riveting, bolting, etc. 7. Heat and surface treatment processes: carburizing, nitriding, electroplating, etc. 8. Advanced processes: EDM, ECM, waterjet, laser machining/ablation, etc. 9. Assembly processes: subassembly of finished products. 1

3 Some Terminology Final products made by the industries can be divided into two major classes: Consumer goods: products purchased directly by consumers (e.g. TV, car, tires etc.) Capital goods: purchased by other companies to produce goods and supply services (e.g. aircraft, machine tools, construction equipment etc.) Production rate: refers to the number of products produced per unit time (ñ), e.g. part/hour. Production variety: refers to different product designs/types that are produced in the plant. Production quantity: refers to the number of products produced annually (n): low production: n < 10 2 medium production: 10 2 <n <10 4 high production: 10 4 < n 2

4 Break-Even Analysis This analysis is conducted to determine break-even point for a product where its production cost (i.e. total cost) is equal to its revenue (i.e. money earned by sales). Ttl Total cost of a product involves fixed and variable costs: Fixed Costs: costs that are not directly related to level of production (e.g..rents and rates, research & development, marketing, machinery, administration, etc.) Variable Costs: vary directly with level of production (e.g. raw materials, labour, tooling, etc.) Sa ales & Co osts Break Even Point PROFIT Variable Costs LOSS Fixed Costs Production Quantity 3

5 Factors in Process Selection 1. Cost of manufacture The most important factor in the selection of manufacturing process and material. Consider the life cycle cost of a product allowing for maintenance and disposal. The unit cost of a part (C) depends upon the material, tooling and labour costs. C C C n C n C L M ~ C M : material cost per unit C C : capital cost of machinery and tooling C L : labour cost per unit time n : production quantity ñ: production rate 2. Quantity of parts (Production Volume) It refers to the minimum number of parts to justify the use of manufacturing process. The concept of economical lot size: the break-even volume (i.e. the optimum production quantity for a product at desired level of production with profits). The concept of flexibility in manufacturing: related with the production variety (e.g. a process can be adapted to produce different products and/or variations of the same product). 4

6 Factors in Process Selection 3. Complexity The complexity of a part refers to its shape, size and type/number of features on it. Most mechanical parts have 3D shape although sheet-metal parts are simply 2D. Parts can also be symmetrical or nonsymmetrical. Many processes will not allow the manufacture of parts with undercuts. Thus, candidate processes are defined based on the complexity of part geometry. 4. Materials Functional requirements (properties of materials) play an important role. Melting point, level of deformation, strength and ductility are usually the chief factors. For instance, the melting point of material determines applicable casting processes. Also, some materials may be too brittle for shaping by deformation processes while others may be too reactive to have good weldability. The next slide shows Prima selection matrix for material and process selection. 5

7 Prima Selection Matrix Courtesy of: Process Selection: From Design to Manufacture, K.J. Swift & J.D. Booker,

8 Factors in Process Selection 5. Required quality of the part The quality of the part is defined by three aspects: 1. Freedom from internal defects (voids, porosity, micro cracks, segregation) and external or surface defects (surface cracks, extreme roughness, discoloration). 2. Improved surface finish (i.e. lower surface roughness) of a part determines its appearance, affects the assembly with other parts, and increases its resistance to corrosion, fatigue and wear. 3. Good dimensional accuracy and meeting tolerances in order to justify the use of selected material and process for the manufacture of part for achieving required functionality without incurring extra costs. Concluding Remarks: The achievement of good quality in above aspects is influenced by producibility of individual parts as well as the assembly of parts together. For this purpose, the design methodologies (DFM / DFA) should be incorporated. 7

9 DFM and DFA Guidelines Design for Manufacturing (DFM) 1. Minimise total number of parts (without making other parts too heavy or complex) 2. Standardise the components (to reduce costs and to enhance quality) 3. Use common parts across product lines (use same materials, parts and subassemblies) 4. Design multifunctional l parts (e.g. a part may serve as a structural t member and a spring) 5. Design parts for the ease of fabrication (affects material selection) 6. Avoid too tight tolerances (to reduce costs without t deteriorating ti the functionality) 7. Avoid or minimise the secondary operations (unless required for special/aesthetic purpose) 8. Utilise the special characteristics of processes (care about built-in in causes or side effects) Design for Assembly (DFA) 1. Minimise the total number of parts (part not need to be assembled is not required in design) 2. Minimise the assembly surfaces (fewer surfaces need to be prepared for assembly) 3. Avoid separate fasteners (snap fits must be preferred wherever possible instead of screws) 4. Minimise assembly direction (design parts to be assembled from one direction) 5. Maximise compliance in assembly (adjust assembly forces required for non-identical parts) 6. Minimise handling in assembly (design parts so that assembly positions are easy to achieve)

10 DFM Casting Guidelines 9

11 DFM Casting Guidelines Prevent shrinkage cavity. 10

12 DFM Sheet Forming Guidelines 11

13 DFM Sheet Forming Guidelines 12

14 DFM Injection Moulding Guidelines 13

15 DFM Machining Guidelines 14

16 DFM Machining Guidelines 15

17 DFA General Guidelines 16

18 DFA Handling Guidelines 17

19 DFA Joining Guidelines 18

20 DFA Insertion Guidelines 19

21 DFA System Guidelines 20