7.2 CRP, Order Promising, and Final Assembly Scheduling

Quick Answer: RCCP checks whether the MPS is roughly feasible using critical resources and a bill of resources. CRP then explodes MRP orders through routings to create detailed, time-phased load profiles by work center. In assemble-to-order environments, final assembly scheduling (FAS) finishes customer-specific configurations, while order promising commits dates using ATP/CTP so sales does not over-allocate supply or capacity.

Material plans that ignore capacity create false due dates. CPIM Domain IV links MRP to capacity validation and to the commercial promise made to the customer. You must know what each capacity tool assumes, how load is calculated, and how ATO fulfillment differs from make-to-stock master scheduling.

CRP versus RCCP

RCCP asks: “If we build this master schedule, will our key resources survive?” CRP asks: “Given the planned and open orders MRP just produced, where are the work-center overloads by week?” Passing RCCP does not guarantee CRP will be clean—component lot sizes, overlapping orders, and scrap can still stack load into the same bucket.

How CRP Builds Load

For each manufacturing order (planned or released), CRP:

1. Reads the routing (sequence of operations and work centers).
2. Multiplies order quantity by setup + run time (and sometimes move/queue estimates, depending on the system’s capacity model).
3. Places those hours into time buckets based on operation start/due logic derived from the order due date and lead-time offsets.
4. Sums hours by work center and period into a load profile.
5. Compares load to available capacity (shifts × crew × efficiency × utilization, minus planned downtime).

Required capacity (hours) ≈ setup time + (run time per piece × order quantity)

Available capacity (hours) ≈ rated hours × utilization × efficiency (definitions vary by firm; exam stems usually give the factors explicitly).

Load Profiles: Reading the Signal

A load profile is a period-by-period chart or table of load versus capacity at a work center.

Overload is not automatically “add overtime.” CPIM-consistent responses include revising order dates, splitting lots, using alternate routings, selecting alternate work centers, outsourcing, changing lot sizes, or adjusting the MPS if the overload is structural. Underload may justify pulling firm demand forward only when material ATP and upstream capacity allow it.

Infinite versus Finite Assumptions

Traditional regenerative CRP is often infinite loading: it shows overload rather than automatically delaying orders. Finite scheduling / finite capacity tools sequence operations so load never exceeds capacity, pushing completion dates out. On the exam, if a question describes CRP producing an overload percentage, the system is signaling a problem for planner action—not silently promising the original due date as feasible.

Final Assembly Scheduling (FAS) for ATO

In assemble-to-order (ATO) environments, modules and options are often planned by MRP/MPS as buildable stock or short-horizon supply, while the final customer configuration is completed only after the order arrives. The final assembly schedule (FAS) is that short-term completion schedule.

FAS responsibilities:

• Translate configured sales orders into assembly orders.
• Sequence final assembly lines by due date, changeover cost, and material readiness.
• Coordinate with order promising so quoted dates match module ATP and line capacity.
• Firm near-term FAS entries to stop MRP nervousness from reshuffling the line.

A classic exam contrast: changing the MPS for a make-to-stock end item replans the whole structure; changing an ATO customer options mix primarily hits FAS and the option-level supply, not necessarily every unrelated module if common parts remain stable.

Order Promising: ATP and CTP

Order promising is the process of committing a delivery quantity and date to a customer. Two related calculations dominate CPIM language:

Simplified discrete ATP idea for a period:

ATP = on-hand (first bucket) or MPS receipt − sum of actual customer orders already booked until the next MPS receipt

(Exact ATP formulas vary—cumulative ATP versus discrete ATP—but the exam concept is the same: do not promise what is already sold.)

Good promising practice:

• Promise against ATP, not against total inventory or total MPS volume.
• Escalate to CTP when assembly capacity or critical components constrain the FAS.
• Keep a demand time fence / policy so near-term FAS and promises are planner-controlled.
• When supply is short, allocate by policy (fair share, priority customers, margin)—do not silently double-book.

Worked Mini-Scenario (ATO Promise)

A configure-to-order pump uses a common motor module. Week 2 ATP for motors is 25. The final assembly line has 40 hours free in week 2; each pump needs 1 hour of final assembly. A customer requests 30 pumps in week 2.

• Material ATP supports only 25 → promise 25 in week 2 unless CTP finds earlier module expediting.
• Capacity would allow 30, but material is the constraint → promising 30 would create a FAS that MRP/CRP cannot honestly support.
• Planner options: split ship (25 then 5), substitute an alternate motor with its own ATP, or move the order to week 3 where ATP recovers.

Linking CRP, FAS, and Promising

1. MPS / module plan validated with RCCP.
2. MRP plans components; CRP flags work-center load issues.
3. Sales books orders using ATP/CTP.
4. FAS sequences actual configurations in the short horizon.
5. Overloads or ATP breaches trigger replanning—not silent overtime assumptions—unless policy authorizes them.

Exam Pitfalls

• Treating RCCP and CRP as interchangeable detail levels.
• Reading a CRP overload as proof the schedule is impossible without considering alternate routings or date moves.
• Promising from on-hand + open orders without subtracting committed customer orders (ATP discipline).
• Assuming FAS replaces MRP in ATO—FAS finishes the product; MRP still plans modules and lower levels.