Chapter 11. Metal-Casting Processes. 3/20/ :032 Design for Manufacturing 1

Transcription

1 Chapter 11 Metal-Casting Processes 3/20/ :032 Design for Manufacturing 1

2 Manufacturing Processes Alternatives Material Removal Processes Forming Processes Assembly Similar to? Examples? And.. Casting Processes 3/20/ :032 :Design for Manufacturing 2

3 Metal Casting Processes The process involves: Pour molten metal into a mold patterned after the part to be manufactured Allow it to solidify Remove the part from the mold Advantages of Metal Casting Processes: Produce part in single step ( near-net shape) Produce large parts Can produce a wide variety of shapes and sizes Complex shapes are possible Internal cavities are possible Any Disadvantages? 3/20/ :032 :Design for Manufacturing 3

4 Examples of Cast Products Note how difficult it might get to produce these parts using other manufacturing processes Fig Fig. Fig dbac Fig /20/ :032 :Design for Manufacturing 4

5 Categories of Metal-Casting Processes Expendable Molds: Typically made out of sand, plaster, ceramics and similar material Such material are refractory i.e., capable of withstanding high temperatures. After casting the mold is broken up to remove the casting Permanent Molds: Made of metals that maintain their strength at high temperatures. Are used repeatedly Designed in such a way that the casting can be removed easily 3/20/ :032 :Design for Manufacturing 5

6 Categories of Metal-Casting Processes Composite Molds: Made of two or more materials (sand, graphite, and metal) in order to combine the advantages of each Have both permanent and expendable portions 3/20/ :032 :Design for Manufacturing 6

7 First: Expendable Mold Casting There s a variety of casting processes that use expendable molds. We will focus on discussing 2 of them in detail: Sand Casting Investment Casting 3/20/ :032 :Design for Manufacturing 7

8 Sand Casting Process outline: Place a pattern (having the shape of the desired casting) in sand to make an imprint Incorporate a gating system Remove the pattern and filling the mold cavity with molten metal Allow the metal to cool until it solidifies Break away the sand metal Remove the casting Example Can we make hollow parts or parts with internal cavities? How? 3/20/ :032 :Design for Manufacturing 8

9 Sand Casting (contd.) Sands Silica sands (SiO 2 ) is widely used as the mold material High melting point Factors affecting sand selection Fine round grains can be closely packed Fine grained sand has lower permeability Mold should have good collapsibility 3/20/ :032 :Design for Manufacturing 9

10 Sand Mold Terminology Figure 11.3 Schematic illustration of a sand mold, showing various features. 3/20/ :032 :Design for Manufacturing 10

11 Finished Casting 3/20/ :032 :Design for Manufacturing 11

12 Sand Mold Preparation (a) Mechanical drawing of part (b & c) Pattern Mounting (d) Core Production 3/20/ :032 :Design for Manufacturing 12

13 Sand Mold Preparation (Cont d.) (e) Cores are pasted (f ) Assembly of the cope half of the mold (g) The flask is rammed with sand (h) The drag half is produced in a similar manner (i) The pattern, flask, and bottom board are inverted; and the pattern is withdrawn 3/20/ :032 :Design for Manufacturing 13

14 Pattern Plate 3/20/ :032 :Design for Manufacturing 14

15 Pattern Considerations/Allowances Shrinkage Allowance (Why?) Machining Allowance (?) Draft Allowance (?) Round corners (?) 3/20/ :032 :Design for Manufacturing 15

16 Demonstration of the Draft Allowance 3/20/ :032 :Design for Manufacturing 16

17 Sand Cores Cores are used for internal cavities and passages Removed from the finished part during shakeout Must be strong, collapsible, permeable, heat resistant Made in a similar manner to mold making Figure 11.6 Examples of sand cores showing core prints and chaplets to support cores. 3/20/ :032 :Design for Manufacturing 17

18 Investment Casting Process Another common casting process with expendable molds. Also known as lost-wax process The mold material and labor is costly Advantages Suitable for high-melting-point alloys Good surface finish Few or no finishing operations thus reducing cost Typical parts Mechanical components such as gears, cams, valves. Lately, titanium aircraft-engine Parts up to 2500 lbs were successfully produced 3/20/ :032 :Design for Manufacturing 18

19 Investment Casting Process (Cont d) Figure Schematic illustration of investment casting (lost-wax) process. Castings by this method can be made with very fine detail and from a variety of metals. 3/20/ :032 :Design for Manufacturing 19

20 Disadvantages of Metal Casting Depending on the casting process used, and specially for expendable mold casting processes discussed in this lecture: Production rate can be slow Finished Casting usually needs finishing operations Casting Defects 3/20/ :032 :Design for Manufacturing 20

21 Casting Defects and How to Avoid them 3/20/ :032 :Design for Manufacturing 21

22 Next Time Permanent Molds Casting Processes Other Technicalities in various casting processes 3/20/ :032 :Design for Manufacturing 22

23 Casting Design Research Process design Process modeling Process simulation Opportunities

24 Casting System Components Design for Manufacturing 2

25 Casting System Components Design for Manufacturing 3

26 Metalcasting Lead Time & Cost Reduction Project Objectives: Define an integrated casting design environment Determine the capabilities of existing software Consider both expendable mold & permanent mold processes Tasks: Complete surveys of software suppliers & users Determine current industrial practice with casting software Evaluate costs & benefits of casting design software Define scenarios for foundry use of software Develop functional design of an integrated casting design environment Design for Manufacturing 4

27 Casting Process Design Part orientation Parting line location Gate(s) and riser(s) design Pattern/mold design Process simulation Design for Manufacturing 5

28 Casting Design Environment Pattern/mold Design Laser Scanning CAE Applications CAD System Dynamics Heat transfer FEM Design optimization Shared Database Part & mold geometry Casting material properties Mold material properties Process types & characteristics Activity Manager Parting line location Allowances & draft Rigging system Tolerance specification Shape constraints Performance Capability Resource availability Time estimation Cost estimation CAM Applications CNC machining Rapid prototyping Process Simulation Fluid flow Heat transfer Solidification Stress growth Defects/Quality Criteria Functions Design for Manufacturing 6

29 Integrated Casting Design Software Environment Design for Manufacturing 7

30 Casting Design Software Functions Design for Manufacturing 8

31 Casting Model Input Parameters Part Geometry Part Material Tolerance & Finish Production Requirements Model Output Casting Geometry Production Cost Solidification Time Stresses & Defects Process Design Casting Process Parting Line Location Gating & Risering Design for Manufacturing 9

32 Casting Process Simulation Casting Simulation Using MAGMAsoft XM35 Rotor Part design Simulation model Simulation results Redesign iterations Design for Manufacturing 10

33 Continuous Casting Research Continuous casting process Workflow production planning IPSCO Caster model process planning Design for Manufacturing 11

34 Continuous Casting Process Design for Manufacturing 12

35 Continuous Casting Model Thickness Width Carbon% Superheat Casting Speed Cooling Rate Neural Network Mean Standard Deviation Design for Manufacturing 13

36 Optimization Scheme Design for Manufacturing 14

37 Questions & Answers Design for Manufacturing 15