CAM and Recent Technology

CAD/CAM integration means that the product data produced in design (geometry, dimensions, tolerances, material, BOM) is used directly in manufacturing planning and control, without redrawing or re-entering it. A single digital product model acts as the common database.

Information flow

 Design requirement
        |
   CAD model (3D) ----> CAE analysis (FEA, CFD)
        |                       |
        v                       v
   Drawings, BOM        Design optimisation
        |
        v
   CAPP: process planning, tool selection
        |
        v
   CAM: tool path -> post-processor -> NC / G-code
        |
        v
   CNC machine / robot / 3D printer ---> inspection (CMM)
        |__________ feedback to design ____________|

Steps

1. The 3D model is finished in CAD.
2. The CAM software reads the geometry (native, STEP or IGES).
3. Features are recognised (holes, pockets); tools, speeds and feeds are selected.
4. Tool paths are simulated and checked for collisions.
5. A post-processor converts the cutter location data to the code of the specific CNC controller.
6. The program is sent to the machine (DNC); inspection results are fed back.

Benefits

• Shorter lead time and fewer errors, since no manual re-entry of geometry.
• Design changes flow to NC programs (associativity).
• Better quality and repeatability, optimised tool paths and material use.
• Allows concurrent engineering, where design and manufacturing work together.
• Basis for CIM, flexible manufacturing and Industry 4.0.

A Manufacturing Execution System (MES) is a computer system that tracks, controls and documents the conversion of raw materials into finished goods on the shop floor in real time. It sits between the planning system (ERP) and the control systems on the machines (PLC, SCADA, CNC).

Position in the automation hierarchy

 Level 4  ERP / business planning (orders, finance)
              |        ^
              v        |  orders, status
 Level 3  MES - execution, scheduling, tracking
              |        ^
              v        |  work orders, data
 Level 2  SCADA / cell control
 Level 1  PLC / CNC / robot controllers
 Level 0  Sensors and actuators, machines

Main functions

1. Detailed scheduling of operations on machines and sequencing of jobs.
2. Resource allocation and status: machines, tools, labour and material.
3. Dispatching production units: releasing work orders to cells.
4. Document control: drawings, NC programs, work instructions delivered to the right machine.
5. Data collection: actual times, quantities, scrap, downtime.
6. Quality management: inspection data, SPC, traceability (lot and serial numbers).
7. Maintenance management and performance analysis (OEE).
8. Product tracking and genealogy.

Role in CAD/CAM

CAD/CAM supplies drawings, process plans and NC programs to the MES, which distributes them (DNC) and returns as-built data. MES gives automation its information backbone and supports CIM and smart-factory systems.

Need for data exchange

Different CAD, CAE and CAM systems store models in different internal (native) formats. Companies, suppliers and customers use different software, so a neutral format is needed to move the geometry without redrawing, with fewer errors and losses. Neutral formats are also used for long-term archiving.

Comparison

Differences

• Scope: IGES transfers geometry only; STEP transfers geometry plus product data (assembly structure, tolerances, materials) and is the modern replacement.
• Solids: IGES has poor solid support; STEP supports B-rep and CSG fully.
• Dimensions and 2D: DXF is best for 2D drawings and laser/plasma cutting; widely read by all 2D software.
• STL: approximates surfaces by triangles; used for 3D printing and rapid prototyping; accuracy depends on facet size.
• Quality: IGES translation often leaves gaps and trimmed-surface errors; STEP is more reliable.
• Standard status: STEP and IGES (frozen since 1996) are standards; DXF and STL are industrial de-facto formats.

STL format

STL describes the surface of a solid by a mesh of triangular facets. Each facet stores the unit normal and three vertex coordinates (in anticlockwise order seen from outside). Two types: ASCII (readable, large) and binary (compact).

Rules:

1. The vertex order follows the right-hand rule, so the normal points outward.
2. Each edge is shared by exactly two facets (watertight mesh); no gaps.
3. All coordinates are positive in older versions; the units are not stored.
4. Finer facets give a smoother surface but a larger file (chordal tolerance control).

Binary layout: 80-byte header, 4-byte facet count, then 50 bytes per facet (12 floats $=48$ bytes + 2-byte attribute).

(a) Facets

Normal $=(\mathbf V_2-\mathbf V_1)\times(\mathbf V_3-\mathbf V_1)$ with vertices ordered anticlockwise from outside.

Example for facet BCD: $(\mathbf C-\mathbf B)=(-10,10,0)$, $(\mathbf D-\mathbf B)=(-10,0,10)$.

$$(\mathbf C-\mathbf B)\times(\mathbf D-\mathbf B)=(10\cdot10-0,\ 0-(-10)(10),\ 0-10(-10))=(100,100,100)$$

and $|\,\cdot\,|=173.2$, giving $0.577$ for each component. It points away from A, so it is outward.

Check: each edge appears in exactly two facets (6 edges, 4 faces, 12 edge uses = $6\times2$).

(b) Binary file size

$$\text{size}=80+4+50\,N$$

Tetrahedron, $N=4$: $80+4+200=284$ bytes.

Model with $N=12\,000$: $84+50\times12\,000=600\,084$ bytes $\approx 0.6$ MB.

Answer: normals (0,0,-1), (0,-1,0), (-1,0,0), (0.577,0.577,0.577); file sizes 284 bytes and 600 084 bytes (about 0.6 MB).

PDES

Product Data Exchange using STEP was a US initiative of the late 1980s (NIST, industry) to define a neutral way of exchanging complete product data, not only geometry. It was developed together with the ISO group working on STEP, and merged into ISO 10303 (STEP). It includes shape, tolerances, materials, assembly structure and life-cycle data, and was meant to replace IGES.

ACIS

ACIS (by Spatial Corporation, originally "Alan, Charles, Ian's System") is a 3D geometric modelling kernel written in C++ and licensed to many software vendors. It handles wireframe, surface and solid (B-rep) modelling, Boolean operations, blending and offsetting. Its native file is SAT (ASCII) or SAB (binary), which is used to transfer solids between ACIS-based systems (for example AutoCAD, early SolidWorks versions).

Parasolid

Parasolid is a B-rep solid modelling kernel (originally from Shape Data, now Siemens). It supports solids, sheets, wires and free-form NURBS surfaces with robust Booleans. Used in NX, SolidWorks, Solid Edge and many CAE/CAM tools. Its transmit file formats are .x_t (text) and .x_b (binary), which allow direct transfer of exact solid geometry between Parasolid-based software without loss.

Kernel-based formats keep exact (not faceted) geometry, so they are better than STL for CAD-to-CAD exchange.

Rapid prototyping (RP), now called additive manufacturing (AM) or 3D printing, builds a part directly from the CAD model by adding material layer by layer, instead of removing it (machining) or forming it.

Process chain

 CAD solid -> STL file -> slicing into layers
      -> build (layer by layer) -> post-processing -> part

1. Create the 3D solid model in CAD.
2. Convert to STL (triangulated surface).
3. Choose orientation and add supports; slice into thin layers (0.05 to 0.3 mm), generating machine code.
4. Build the layers on the machine.
5. Post-processing: remove supports, clean, cure, sand, infiltrate or heat treat.

Two common processes

• Fused deposition modelling (FDM): a thermoplastic filament (PLA, ABS) is melted in a heated nozzle and deposited along the layer path; the layer solidifies and the platform moves down. Low cost, good for prototypes.
• Stereolithography (SLA): a UV laser traces the cross-section on a bath of photopolymer resin, curing it layer by layer; high accuracy and surface finish. (Others: selective laser sintering (SLS) for powder, laminated object manufacturing (LOM), 3D printing with binder.)

Advantages

• Very complex shapes (internal channels, lattices) with no tooling.
• Fast model for design review and fit checks; lower cost for one-offs.
• Direct link from CAD, with little human work; low waste.

Limitations

• Stair-step surface finish; STL approximation errors.
• Limited materials and strength; anisotropic properties.
• Slow and costly for large production runs; size limits.