Computer-integrated manufacturing and additive manufacturing

Why it matters

Modern vehicle plants run on computer integration: designs flow from CAD into CAM tool paths, robots weld and paint bodies, automated guided vehicles feed flexible machining cells, and production data is tracked in real time. Additive manufacturing (AM) has moved from prototypes to jigs, fixtures, low-volume and lightweight production parts (brackets, ducts, conformally cooled mould inserts). Engineers are expected to know what each technology does, when it pays, and how to estimate lead time and build time.

Key ideas

Computer-integrated manufacturing (CIM) links design, planning, production, quality and business functions through shared databases and networks, so information is entered once and used everywhere.

• CAD – geometric modelling (wireframe, surface, solid), drafting, and analysis (FEA, kinematics).
• CAM – tool-path generation, post-processing to G-code, NC verification; DNC links machines to a central computer.
• CAPP (computer-aided process planning) – variant (retrieves and edits a standard plan for a part family, using group-technology codes) or generative (creates a plan from part features and decision logic).
• Group technology (GT) – classifies parts into families with similar shape or processing (coding systems such as Opitz); the basis of cellular manufacturing, where machines for one family are grouped into a cell, cutting set-ups, material movement and lead time.
• FMS (flexible manufacturing system) – CNC workstations, an automated material-handling and storage system (conveyors, AGVs, pallet changers) and a central computer that routes parts; mid-volume, mid-variety production.
• AS/RS (automated storage and retrieval) and AGVs move and store material.
• Industrial robots – Cartesian, cylindrical, polar (spherical), SCARA and articulated configurations; the work envelope, payload, repeatability (usually much better than absolute accuracy) and the end effector define the application – spot welding, painting, handling, assembly.
• PLCs sequence machines; CMMs and machine vision automate inspection; MRP/ERP plans materials and capacity.
• Industry 4.0 adds sensors, connectivity, data analytics and digital twins.
• Automation choice: fixed (hard) automation for very high volume and low variety (transfer lines for engine blocks), programmable automation for batches, flexible automation for mixed models without changeover losses.

Production metrics. Manufacturing lead time is dominated by non-operation time (waiting, moving, queuing), which is why cells and FMS reduce it so much. Availability measures how much time equipment is ready to work; utilisation measures how much of its capacity is used.

Additive manufacturing. Parts are built layer by layer directly from a 3-D model. The process chain:

1. CAD solid model → export as a tessellated file (STL, or the newer 3MF/AMF);
2. choose orientation and generate supports;
3. slice into layers and generate each layer's path;
4. build;
5. post-process – remove supports, cure, clean, heat treat or HIP, machine critical faces, finish.

AM process categories (ISO/ASTM 52900).

• Vat photopolymerisation – SLA (UV laser) and DLP (projector) cure liquid resin; fine detail and finish.
• Material extrusion – FDM/FFF; thermoplastic filament through a heated nozzle; cheap; anisotropic strength (weak between layers).
• Powder bed fusion – SLS for polymers (no supports needed, the unsintered powder supports the part); SLM/DMLS and electron-beam melting for metals (Ti, Al, Ni alloys, steels).
• Material jetting – droplets of photopolymer, multi-material and colour.
• Binder jetting – a binder glues powder; sintered afterwards for metals; sand moulds and cores for casting.
• Directed energy deposition – powder or wire fed into a laser, electron-beam or arc melt pool; repair and large parts.
• Sheet lamination – bonded or ultrasonically welded sheets (LOM, UAM).

Strengths and limits of AM. Strengths: complex internal channels, lattices, topology-optimised light parts, part consolidation, no tooling, customisation and short lead time for small quantities. Limits: slow build rates and high cost per part at volume, size limits, stair-stepping on inclined surfaces, support removal, anisotropy, porosity and residual stress (metal parts often need stress relief or HIP), and qualification of material properties.

Formulas

MLT = n_o·(T_su + Q·T_c + T_no) Manufacturing lead time for a batch of Q parts (h), assuming the whole batch moves together between operations; n_o = number of operations, T_su = set-up time per operation (h), Q = batch size, T_c = cycle time per part per operation (h), T_no = non-operation time per operation (h).

A = (MTBF − MTTR) / MTBF Availability (fraction); MTBF = mean time between failures (h), MTTR = mean time to repair (h).

N_L = H / t Number of layers; H = build height (mm), t = layer thickness (mm).

Q̇ = w·t·v Volumetric deposition rate for extrusion AM (mm³/s); w = bead (road) width (mm), v = nozzle speed (mm/s).

T_build ≈ V / Q̇ + N_L·t_L Approximate build time (s); V = deposited volume (mm³), t_L = per-layer overhead (layer change, recoating) (s).

c = t·|cos θ| Cusp (stair-step) height (mm) on a surface whose normal makes angle θ with the build direction; vertical walls (θ = 90°) have no stair-step.

Worked examples

Example 1 (standard) – FDM build time. A 120 mm tall part has 50 cm³ of deposited material. Bead width 0.4 mm, layer 0.2 mm, nozzle speed 60 mm/s, layer-change overhead 2 s per layer.

1. N_L = H/t = 120/0.2 = 600 layers.
2. Q̇ = w·t·v = 0.4 × 0.2 × 60 = 4.8 mm³/s.
3. Deposition time = 50 000/4.8 = 10 417 s.
4. Overhead = 600 × 2 = 1200 s.
5. T_build = 11 617 s ≈ 3.23 h. Halving the layer thickness doubles the layer count and halves Q̇, so the build time roughly doubles while the stair-step height halves.

Example 2 (GATE level) – lead time, availability and cusp height. (a) A batch of 50 parts needs 5 operations, each with 2 h set-up, 6 min cycle time per part and 8 h non-operation time. MLT = n_o·(T_su + Q·T_c + T_no) = 5 × (2 + 50 × 0.1 + 8) = 5 × 15 = 75 h, of which only 25 h is actual machining – non-operation time is 40 h (53 %). (b) A cell with MTBF 200 h and MTTR 10 h: A = (200 − 10)/200 = 0.95. (c) SLA with 0.1 mm layers, surface normal at 60° to the build direction: c = 0.1 × cos 60° = 0.05 mm.

Common mistakes

• Treating CIM as "CAD + CAM" only; it integrates planning, control, quality and business data too.
• Confusing variant CAPP (retrieve and edit) with generative CAPP (create from logic).
• Assuming repeatability equals accuracy for robots.
• Thinking AM is always cheaper; it wins at low volume and high complexity, not for simple parts in large numbers.
• Forgetting supports and post-processing when estimating AM cost and time.
• Using STL as a CAD format for editing – it contains only triangles, no design history or exact geometry.
• Mixing hours and minutes in the lead-time equation (6 min = 0.1 h).

For GATE ME

Expect conceptual and matching questions: CIM components, CAPP types, group technology and cellular layouts, FMS elements, robot configurations, fixed vs programmable vs flexible automation, AM process categories with their raw material and energy source, and the STL/slicing chain. Simple numericals may involve lead time, availability, number of layers, deposition rate and build time. Practise matching each AM process to its feedstock (liquid resin, filament, powder, sheet, wire).

Quick check

1. Which AM process cures liquid photopolymer with a UV laser?
2. What does an STL file contain?
3. Which CAPP approach retrieves a standard plan for a part family?
4. Number of layers for a 30 mm part at 0.1 mm layers?
5. Availability for MTBF 100 h and MTTR 5 h?

Answers: 1. Stereolithography (SLA); 2. A triangulated (tessellated) surface mesh; 3. Variant CAPP; 4. 300; 5. 0.95.