Part HD head control arm Quality characteristics Dimension: height, width, wall thickness Mechanical properties of materials: hardness, brittleness, and porosity. Machining Dimension: holes, grooves, and cuts Processes produces the complicated geometries with high dimensional accuracy (in near netshape). It involves forcing molten metal (in this case, probably aluminum) into a steel die cavity at pressures ranging from 0.1-100 ksi. The geometry of the control arm after the die casting process is determined by the geometry of the die tooling. Surface finish and geometry will also be determined by molten temperature, casting pressure. Machine states: casting pressure, machine temperature ( oven temperature ), clamping force, and tooling temperature. Machine properties: thermal conductivity of tool, surface finish of tooling, and geometry of tooling (sharp edges, thin walls, etc.). Material states: material temperature, molten flow rate, molten metal pressure, solidification front, and material stresses. Material properties: melting temperature of material, stress-strain properties, thermal expansion characteristics, viscosity, and heat conductivity. Machining performs the finishing operations such as drilling holes, making cuts, surface finishing, and shaving to proper dimension. This can be done on a manual mill or a CNC machine. Here the determinants of part geometry will be the tool path of the mill combined with feed, spindle speed, cutting tool material, etc. Equipment states: feedrate, spindle speed, spindle torque, workpiece temperature, coolant temperature, coolant flow rate, tool holder position, and clamping force. Equipment properties: tool geometry, tool material, structural stiffness, damping, natural frequency, and structural geometry. Material states: stresses and Control variables oven temperature, casting pressure, clamping force, and tooling temperature. Machining feed, spindle speed, tool holder position, and coolant flow rate/temperature (if necessary). Energy interactions : heat transfer and solidification occurs throughout the part and the interface between the part and the tool (mold). The energy transfer is thermal. The mode of transfer is parallel. Machining: material removal occurs locally. The tool plows through the workpiece to remove material. The area of interaction between the tool and the workpiece is much smaller than the characteristic area of the workpiece itself. The energy transfer is mechanical. The mode of transfer is serial. Sources of variation Die wear alters the surface finish characteristics, the heat transfer from the metal to the mold, and the flow of molten metal that also affect the heat transfer characteristics of molten metal. Impurities in the alloy affect viscosity and, hence, the flow and heat transfer characteristics of molten metal. Machining machine tool vibration/chatter, cutting tool wear, build-up edge on cutting tool. 1 of 8
Fuel injection throttle body Cantilever beam accelerator Dimension, surface finish Mechanical properties of materials: hardness, brittleness, and porosity. Machining Dimensions, surface finish Geometry: beam length and width/height (crosssectional area) to achieve desired deflection for acceleration measure. Clearance for unobstructed beam deflection is also critical. workpiece temperature. Material properties: stress-strain properties, porosity, and heat conductivity. SEE ABOVE SEE ABOVE SEE ABOVE SEE ABOVE The part is made through a series of deposition and etch cycles using photolithography and wet chemical etching, respectively. A blank substrate is taken as the base. A deposition step continues to build up a sacrificial layer. This layer is then coated with a mask that is subsequently patterned (photolithography). The beam material is then deposited. An etching/release step eats away the exposed mask as well as part of the sacrificial layer along directed crystalline planes (wet chemical etching). Geometry is determined through control of deposition/etch rates by controlling the chemical concentration of the agents as well as the duration of deposition/etch. Accuracy and resolution of the exposed mask is also very important as it determines which parts of the materials are exposed to etch steps. Proper selection of base materials also plays a large part as it partially determines the controllability of the etch reaction (speed and direction). Photolithography. Equipment states: flow of masking agents, chemical potential for mask exposure, proper temperature. Equipment Deposition/etching material concentration and temperature. Improper mask tolerances create wrong size parts. Unexposed/underexpo sed regions cause wrong geometry. Local variations in chemical concentration will cause uneven reaction rates. Temperature variations will change reaction rates (local and global effects). Wrong crystalline structure will cause chemical etching in undesired directions. Operators will cause variations by changing concentrations and reaction times. 2 of 8
Disk brake rotor Sand casting: Dimension: diameters according to specifications. Material properties: bubbles/porosity, residual stresses, hardness, brittleness/ductility Machining: Dimensions (roundness, length, width, height, etc.) according to specifications. Surface finish, flatness. Material properties: properties: clean environment, geometric sizing of dispensing nozzles and pattern creation. Material states: chemical potential and extent of reaction. Material properties: mask thickness and viscosity. Wet Chemical Etching. Equipment states: pressure and flow of reactive agents (deposition/etch reactants supplied into reaction chamber), proper reaction temperature. Equipment properties: chamber size and nonreactivity with process materials, dispersion of chemical materials, cleanliness. Material states: chemical potential and extent of reaction, proper reaction temperature. Material properties: proper material composition/structure and beam stiffness. Sand casting: (process principle determinants of part geometry): (i) Produce master pattern dimensional accuracy of pattern, draft angle; (ii) Create the sand mold (2 part) of pattern density of sand pack, sand grain size & composition; (iii) Create the flask, risers, sprue diameter of sprue, flow rate of pour; (iv) Remove the pattern and close & clamp the mold clamp force, dimensional accuracy of mold; (v) Pour molten material material properties, temperature; (vi) Cool the part time, ambient temperature, material properties; (vii) Open the mold and remove part speed of opening; and (viii) Remove the sprue and runners clean removal. Equipment states: ambient temperature (if the factory is climate controlled), mold temperature, and clamp force of mold. Equipment properties: draft angle, geometry of mold, grain size/composition, permeability, pattern geometry, heat expansion coefficient of sand and heat transfer coefficient of sand. Material states: Sand casting: (initial) mold temperature, molten alloy (initial) temperature, pouring flow rate, clamping pressure, and cooling time (An indication of process completion, cycle time is also rate-depending.) Machining: SEE ABOVE Sand casting: variations in material properties: minor changes in the material viscosity can result in major changes in how well the mold fills, variation in the heat transfer properties of the mold alters the temperature in molten metal that causes changes in its viscosity and the way the mold fills. Changes in heat transfer property effect cooling rate that can cause porosity. Wear on the mold wall affect the flow of molten metal and the heat 3 of 8
Tape drive Head Beam Assemnly Surface finish, weight, proper location of datum surfaces temperature profile, flow rate during filling, pressure of molten metal during filling, and solidification front (crystallization of alloy). Material properties: viscosity, heat transfer coefficient, impurities, density of chosen material, and heat expansion coefficient of alloy. Machining (process principle determinants of part geometry): (i) Position location feature in a mill equipment fixture accuracy; (ii) Bore center hub & screw holes depth of tool, spindle speed, tool diameter, equipment properties, tool bit properties; (iii) Remove part & fix on lathe equipment properties; (iv) Turn the part spindle speed, feed speed, traverse speed, tool bit properties & position; and (v) Remove part. Equipment states: feedrate, spindle speed, spindle torque, tool temperature, coolant temperature, coolant flow rate, tool holder position, and clamping force. Equipment properties: tool geometry, tool material, structural stiffness, damping, natural frequency, and structural geometry. Material states: stresses. Material properties: stress-strain properties, porosity, and heat conductivity. Injection Molding: The primary determinant of the injection molding process is the shape of the mold cavity. Secondary determinants include the resin state and composition, design of the gating and mold flow paths, injection pressures and temperatures and the mold cooling characteristics. Equipment states: temperature (preheat chamber), control force, screw velocity. Equipment properties: Mold cavity geometry, thermal mass and coefficient through flow path, cleanliness and surface conditions. Material states: temperature, injection pressure, flow rate. Material properties: viscosity, thermal Injection Molding: mold shape, temperature, pressure, fill volume. Machining: toolpath, velocity. See above transfer properties of the mold. Machining: SEE ABOVE See above 4 of 8
5 of 8 coefficient, composition of material. Machining: The primary determinant for the machining operation is the shape, sharpness, rotational velocity, and trajectory of the endmill with respect to the fixture datum. Also important is the consistency of HBA position with respect to the fixture datums (and by extension to the tool location). Equipment states: rotational velocity, force, temperature, heat flux. Equipment properties: mill and fixture geometry, stiffness, damping, endmill geometry. Material states: bending stress, strain in workpiece. Material properties: initial geometry, material composition.
In the following table, we will discuss the control techniques for the above processes. Process Machining Photolithography & wet chemical etching Sand casting Control techniques Machine control for injection, machine control to regulate mold temperature, machine control to regulate temperature of molten metal. Statistical process control to monitor any variations in the raw material quality and the effect of any other common causes on the output. We also need standard operating procedures. Machine control for tool trajectory, machine control for cooling, SPC to monitor variations in the raw material quality, the effect of tool wear, and the effect of other common causes on the output. We need standard operating procedures. Statistical Process Control and Run by Run control. SPC detects variations in material and equipment properties. We also need standard operating procedures. Machine control to regulate the melt temperature. Machine control to regulate the filling process. If filling is done manually, then we need standard operating procedures to provide guidelines for consistency in the process. SPC is used to detect variations in the material properties as well as in the machine properties (e.g., mold wear) and other common causes that influence the outputs. Process taxonomy: Process Taxonomy Spatial Resolution Characteristic time Machining Serial removal High High; however, cycle time can be low depending on complicated geometry Sand casting Photolithography Wet chemical etching Parallel solidification forming Parallel photochemical removal Parallel chemical removal Parallel solidification forming Medium to, cycle time is approximately equal to characteristic process time to medium to medium to medium 6 of 8
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