Task 1: Manufacturing system
A max 3000 words report is required for this assignment. There is no need to write a formal report. Please only provide the answers for each question and make sure you quote the question number for your answers in the report.
- Design for Manufacturing (20 marks)
Machining vices are widely used for holding parts for machining operations. As shown in Figure 1, a vice normally has two jaws. The surface on jaws that contacts parts is often flat and hardened. These make the vice incapable of holding complicated parts for machining and may mark on the finished part surfaces. In order to hold a specific shape of parts, soft jaws using softer materials such as Aluminium are machined to a specific shape and mounted on the original jaws.
Figure 1: Soft jaws on machine vice
Assume that you are a machinist and are given a job to machine a series of precision cylindrical bars with sizes ranging from 30mm to 50mm in diameter. Your task is to design soft jaws to replace the existing soft jaws shown in Figure 1 to hold the cylindrical bars for machining.
The requirements of your design are as below:
- The cylindrical parts are held vertically;
- The cylindrical parts should have loading repeatability, in other words, the CNC machine knows the part position after the cylindrical bar is clamped in the vice.
- You can assume the cylindrical bars are sufficiently long to be held in the vice.
- Since the cylindrical bars are precision component, reasonable accuracy and surface finish is required for critical surfaces of your soft jaws (e.g IT grade 7 or 8, surface finish Ra3.2 or Ra6.3 for the critical surfaces);
The CAD models of the machining vice and the existing soft jaw have been uploaded to mystudies->ME545->study materials->Semester 1->Assignment
Your soft jaws must fit on the fixed and movable jaws of the vice.
- Provide two screen shots of the assembly of the soft jaws on the machine vice holding the cylinder of the maximum diameter (ɸ50) and of the minimum diameter (ɸ30) respectively; The machine vice, cylinder and soft jaws (consider to use different colour to represent the vice, cylinder and soft jaws respectively) must be clearly shown in the screen shot;
- Provide an engineering drawing showing geometry, dimension, dimensional and/or geometrical tolerance and surface finish of the soft jaws;
- Assume 3 axis CNC machining centre is used to machine the soft jaw from the block size to the shape that you have designed. Suggest how DFM principles are applied in your design, e.g. what do you do to reduce the machining setup, machining time, reduce the number of tool change etc, reduce machining cost. (You may want to work this question after you have completed task 1.3)
- The design satisfies the loading repeatability,
- Capable of holding a series of cylindrical bars with sizes ranging from 30mm to 50mm in diameter;
- Correct dimension and tolerance so that the soft jaw can be assembled on the machine vice;
- Correct surface finish and tolerance so that the soft jaw can be put on the machine vice to hold the precision cylinder bars accurately
(V) Justification of how DFM principles are applied in your design
1.2 Fixture Design (20 marks)
1.2.1 Fixture design for 3 axis machining
You are asked to design modular fixture(s) using standard fixture elements (locators, clamps etc.) to hold the soft jaw you have designed in Task 1.1 for machining of the soft jaw. If you have designed two different soft jaws to be mounted on the fixed jaw and movable jaw respectively, you only need to do the fixture design and the subsequent Computer Aided Manufacturing (SolidCAM) simulations for the soft jaw on the fixed jaw.
You are supposedto use a 3 axis CNC machining centre to machine the stock material of the soft jaw to your designed final shape of the soft jaw.
The size of the stock material in relation to the target geometry envelop of the soft jaw is shown in Figure 2; The areas of between stock material (dash lines) and the target geometry (solid lines) in Figure 2 are rest material to be m
Front view size view
Figure 2 Stock and target geometry envelop
- All surfaces must be machined;
- Specify the number of setup for the CNC machining and for each of the setup, identify the features to be machined,the stage geometry of the component after each of the setup(The number of set upindicateshow many times the components have to be takenout and put backagain on the machining centre to reposition the components for machiningoperations)
- Design a module fixture composed of locators and clamps for each of the setup;
- You are encouraged toreuse thefixture elements (locators and clamps) for different setups;
- The locators and clamps should be mounted on a rectangular base plate (700X700X50); You may want to drill holes and do some machining on the modular base plate for the locators and clamps to be mounted on the modular base plate to hold the soft jaws.
- When the components (the soft jaws) are located using the modular fixture on the a rectangular base plate ((700X700X50), the components should have loading repeatability which means the component is located, namely, when the component is taken off from the fixture and put back again within the fixture, it will stay at the same position.
- Try to use standard locators and clamps asmuch aspossible;Note: Thestandard components you may need include: dowel pins, side clamps, top Clamps etc.
- You maybe ableto downloadsome of CADmodels fromthe following websites which show catalogues of components, dimensions and prices. (please note the dimensions for the products are often in imperial, you will need to convert them in metrics;))
7. If not possible to download the CAD model of modular fixture elements, you should build the rough CAD models yourself based on the dimensions provided by the websites.
8 If you think it is better to make customised locators/clamps rather than standard ones, provide engineering drawing for your own design and your justification for this.
- For the fixture design of each setup, provide:
- screenshots of the 3D assembly CAD models showing the positions of all locators, clamps and module base plate in relation to the component (your designed soft jaw) clearly (Consider to use different colour to show component (your designed soft jaw) and ensure all locators/clamps are visible);
- use screenshots to the soft jaw’ stage geometry (how the geometry is changed from the stock materials to the final target geometry after each setup.)
- Provide the screen shot of the modular base plate that has been customised by you for your fixture design;
- Provide a bill of materials including part number, quantity, material and supplier for all parts used for all setups of machining including locators, clamps, component, modular base plate;
- Discuss how many setups will be needed to machine the soft jaw you designed shown in Figure 2 if a 5 axis machining centre instead of a3-axis machining centre is used. No need to go to detailed fixture design, justmention the numberof setups and the features to be machined and the operations (drilling, end milling, facing etc.) in each setup and explain why.
Marking criteria for task 1.2 (20 marks)
Selection and position of of clamps assembly 3 marks
Selection and position of locators 3 marks
In total 6 marks
|The number of setups and fixtures 2 marks|
Machining efficiency 4 marks
|All the features on the part can be machined using the proposed fixture 3 marks|
|Presentation and bill of materials 2 marks|
Discussion about fixture for 5 axis machining 3 marks
1.3 SolidCAM/G codes (20 marks)
|Chip load F (mm/tooth/rev)||
Cutting speed (Surface speed)
|Max Depth/pass||Radial depth (Step over)||Operation|
Drill (2 teeth), sizes:
From 1mm to 20mm
F=0.001 × Diameter of drill
e.g. if Diameter=5, then F=0.005mm/teeth/rev
|100||N/A||N/A||Drilling of the holes|
|Ø50 Face Mill, 6 teeth, HSS||0.01mm/teeth/rev||
|3mm||40% cutter diameter||Face milling|
End mill, Solid Carbine-coated 4 teeth;
Tool size (diameter): 6mm, 8mm, 10mm, 12mm; 16mm; 20mm
6mm tool: 0.05
8mm tool: 0.06
10mm tool: 0.10
12mm tool: 0.10
16mm tool: 0.10
20mm tool: 0.15
40% cutter diameter for rough operation
30% of diameter for finish operation
|Pocket and profile|
Table 1: Cutting parameters
In this task, you are requested to conduct Computer Aided Manufacture (CAM) simulation for the machining of the soft jaw you designed in task 1.1 using the fixture you designed in task 1.2 on a 3 axis CNC machining centre to machine the soft jaw from the stock size to the target size (the final size of the soft jaw). The machining operations may include holes, face, pocket and profile. The difference between the stock size and the target geometry envelope is shown in Figure 2.
You may use SolidCAM for the CAM simulation or write the G codes manually for the machining of soft jaw with the machining parameters is shown in Table 1. You will need to decide the tool size and its corresponding cutting parameters for the machining. All surfaces must be machined and the features that have surface finish and tolerance requirement will need finish machining with 0.5mm rest material on the wall and/or floor respectively in addition to rough machining. You should avoid the collision between the cutter(s), component(s) and fixture during the machining.
- Provide screenshot for the SolidCAM simulations
- Screenshot for the machining operations tree, e.g. below
- Screenshot of the tool path for each setup;
- Screen shot of the rest material for each setup (SolidCAM manager-> Operation->simulation-> rest material), e.g. the screen shot below
- Screen shots for the cutting parameters including feed rate, spindle speed, depth of cutting, radial depth of cutting shown in Table 2 in 1.3.2 for a feature on the soft jaw you have designed that needs both rough and finish machining;
- Complete the below table
Table 2: Cutting parameters for various machining features;
|Feed rate (mm/min)||Size of tool (mm)||Spindle speed (RPM)||Depth of cutting (mm)||Radial depth (Step over)(mm)||MRR(mm3/min)|
|Add other features as appropriate|
- Summarise the machining strategy (e.g. the number of setup, the operations for each setup) You do not need to model fixture in your SolidCAM simulations, however, you must demonstrate your awareness of fixture position and show how the potential collision between fixture, workpiece and cutter is avoided in your report;
- Explain how you get the values in Table 2;
- If you want to shorten the cutting time to half and, what will you do assuming the same amount of setup time? What are its impacts on the machining quality (e.g. dimension inaccuracy caused by deformation and surface finish) and tool life?
- Estimate the rough total energy required assuming the specific energy for aluminium is 15kilowatt-hour per kilogram.
Marking criteria for task 1.2 (20 marks)
Correctness of SolidCAM simulation for the machining operations 6 marks
Machining strategy 3 marks
Calculation of machining parameters 3 marks
Calculation of MRR 3 marks
Shortening machining time 3 marks
Energy estimation 2 marks
1.4 Manufacturing processes (15 marks)
Figure 3 Keyway
A key is a piece of metal used to connect a rotating machine element to the shaft. A key prevents a relative rotation between the two parts, and may enable torque transmission to occur. For a key to function properly, both the shaft and rotating elements (gear, pulley and coupling) must have a keyway and a keyseat. Usually the term keyseat is referred as a groove or pocket on a shaft, and a keyway is a slot in a hub in which the key fits into. Assume that you are a machinist who need to machine the stock materials (cylinder rods Ø65 of that are sufficiently long) to final target geometry as shown in Figure 3(b).
- Describe the machining strategy to machine the cylinder from stock material to target material using conventional machining.
- Assume the spindle speed is 2000RPM and the nose radius of the cutter is 0.02mm, recommend the feed rate (mm/revolution) for conventional machining to achieve the surface finish of the external surface?
- Assume the material for the part is tool steel, can the parts be machined using non-conventional machining processes, if so, would you recommend a process? If the parts made of tool steel are to be 3D printed, what are the possible 3D printing processes? How the surface finish and the sharp corner for the key way are achieved?
1.4.4 Assume your company has got an order for 50,000 cylinders with internal keyway, your client would like to agree a sampling acceptance plan with your company. For Lot size N=1000, three sampling plans are proposed,
Plan 1: sample size = n = 10, reject if number defectives C> = 1.
Plan 2: sample size = n = 20, reject if number defectives C >= 2
Plan 3: sample size = n = 20, reject if number defectives C> = 1
Create the Operating Characteristic (OC) Curves for these three sample plans and show the 5% producer’s risk and 10% customer risk on the QC curves and identify the best for the manufacturer if the producer wants to have <5% producer’s risk and the best for the customer if the customer wants 10% customer’s risk
Manufacturing quality control (5 marks)
Company Delta Plastics is a market leader in the design and manufacture of plastic container, primarily for kitchen and household use. Delta’s R&D group has recently developed a new plastic material which the market team believed could revolutionize the industry. So they pushed for rapid production in spite of objection from Joe De Costa, head of Manufacturing, stating that the new material is susceptible to cracking.
Exactly one month after production, the latest production quality report was produced showing weekly defects for products made with the new materials (dubbed by marketing as “super plastic”) versus the standard material. Joe De Costa was nervous. Even if there was a difference in quality, he was not sure what action to take.
Use one or more of the quality tools you have learned in the lectures and tutorials to analyze the defects in the case, and help Joe to decide.
1.4.5 Are there more defects associated with the super plastic versus the standard material?
1.4.6 Is the new materials susceptible to cracking? (3 marks)
Task 2: Measurement lab (25 marks)
Venue: Metrology lab, Glass room, AEB106
Measurement room, the glass room, upstairs of Advanced Engineering Building
- Read this brief carefully before coming to the lab
- Up to 6 students per session;
- Each session is composed of three tasks:
Task 2.1: Measurement of pins using micro meter and Vernier calliper
Task 2.2: Measurement of Surface finish
Task 3.3 Measurement using Coordinate Measurement Machine;
- Two in pair for each task and each student must complete all the three tasks
6 students per group
|Session 1(0-20minutes)||Session 2 (25-45minutes)||Session 3( 50-70minutes)|
|Student 1 & student 2||Pin measurement (Task 2.1)||Surface finish measurement (Task 2.2)||CMM measurement (Task 2.3)|
|Student 3& Student 4||Surface finish measurement (Task 2.2)||
|Student 5 & student 6||
|Surface finish measurement (Task 2.2)|
Please read this brief and watch the videos of the measurement before the lab. The video of the three measurements is available at my studies->semester 1-> measurement lab
In this laboratory you will be required to use the following measuring instruments to measure the given specimens.
- Digital micrometer
- Digital vernier calliper
- Surface finish measurement device (Mitutoyo Surface Roughness Tester SJ210 Surftest)
- Coordinate measurement machine
Task 2.1 Pin measurements using a digital micrometer and vernier calliper
Figure4: Key dimensions of pins
The manufacturer produced a small batch of the pins to check the dimensional accuracy before mass production. Assume that you are the inspectors of the factory and are requested to randomly select 15 samples and measure the two critical dimensions in Figure 4 respectively using Digital vernier calliper (accuracy: 0.01mm) and digital micrometer (accuracy: 0.001mm).
If the process capability Cp>1.3 and Cpk>1 for both diameter and length, the manufacturer will go for mass production, otherwise, the manufacturer shall increase the manufacturing accuracy which will incur additional costs.
Figure 2 (a) Figure 2 (b)
Requirements and marking criteria for lab report for task 2.1: (12 marks)
- Data process:
- Based on the measurement data of the diameter and length of the pins shown in Figure 2 (b) you take at the measurement lab, fill the table below. (4 marks)
- Create a X bar control chart for both diameter and length of the pins based on range and statistic factor A2 and draw a conclusion whether or not the machining processes are in control, and provide your justification for this;
- Calculate standard deviation and process capability Cp and Cpk and make recommendation whether or not the manufacturer shall go for mass production;
- Explain why there are significant process variation for the length compared to that for the diameter? (2 marks)
Task 2.2: Measurement using surface finish device (in total 7 marks)
Surface roughness also called surface finish plays an important role in determining how a real object will interact with its environment. Rough surfaces usually wear more quickly and have higher friction coefficients than smooth surfaces. Roughness is often a good predictor of the performance of a mechanical component, since irregularities in the surface may form nucleation sites for cracks or corrosion. Although roughness is usually undesirable, it is difficult and expensive to control in manufacturing. Decreasing the roughness of a surface will usually increase exponentially its manufacturing costs. This often results in a trade-off between the manufacturing cost of a component and its performance in application. There are many factors affecting the surface finish. In terms of machining parameters, one of the most important factors affecting the surface finish is the feed rate.
The purpose of this task is to study the effects of machining parameter feed rate on surface finish. Three samples shown in Figure 3 have already been machined employing different feedrate as shown below on the Hurco CNC machining centre located in E19;
|Chip load||Cutting speed||Cutter||Material|
Spindle speed: 2000RPM
Diameter of cutter 80mm;
Sample 1 Sample 2 Sample 3
Figure 3: Samples for surface finish measurement
In the lab, you will need measure 4 different positions on each of the three samples using the surface finish measurement machine; Both Ra and Rz are measured on these 4 points for each sample.
Figure 4: The rough four positions for surface finish measurement
Requirements and marking criteria for lab report for task 2.2: (in total 7 marks)
- Based on the data you take in the lab, fill the table below. (3 marks)
|Ra||Position 1||Position 2||Position 3||Position 4||Average||Range|
|Rz||Position 1||Position 2||Position 3||Position 4||Average||Range|
- Based on your measurement data, comment on measurement uncertainty and the factor affecting the uncertainty, and quantify the impacts of feed rate on surface finish of machined parts; Your comments must be backed with the measurement data. (4 marks)
Task 2.3. Measurements using Coordinate Measurement Machine
- The coordinate measurement machine (CMM) is very delicate and expensive and so you must use it with extreme care. The accuracy of the CMM is around 0.005mm.
- The measurement block shown below is machined by the CNC machine at E19 based on the engineering drawing shown in Appendix 1.
- The CMM measurement includes three steps: (a) creation of the measurement coordinate system by measuring the top surface, the front surface and left side surface; (b) measurement of the features (slots, pockets and holes); (c) generation of CMM measurement data.
- The measurement points on the measurement features (circles and points) are shown in Appendix 2.
- All your measured readings will be captured by the computer and from these you can determine the various dimensions.
Requirement and marking criteria for a lab report for task 2.3 (In total 6 marks)
- Fill the table shown in Appendix 3 to compare the measurement data with the design data shown in the engineering drawing (Appendix 1). (4 marks)
- mark reduction for each mistaken, 4 marks for no mistake)
2.3.2 Draw a conclusion whether or not the dimension quality of the block is satisfactory and provide your justifications; (2 marks)
Appendix 1-Engineering drawing of the part for fixturing, machining and measurement
Appendix 2 CMM measurement point
Appendix 3: CMM measurement data in comparison with the nominal data