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Engineering process instruction (EPI) template

An engineering process instruction (EPI) is the engineering definition of a process: what it covers, the equipment and materials it uses, the parameters it must run within and their limits, how it was validated or qualified, and what counts as an acceptable output. Operators do not work from it directly; the work instructions for each station are written from it. Some companies call it a process specification or engineering specification, and no standard defines the name. Where a company also uses a manufacturing process instruction (MPI), the EPI says what the process is and why, and the MPI says how the operator does it. Page 1 of this template covers the purpose and scope, references, equipment and materials and a table of parameters with nominal, lower and upper limits, how each is set and monitored and what to do if it goes out. Page 2 has the process sequence and the validation or qualification steps with acceptance criteria and results; page 3 the product acceptance criteria, change history and approvals.

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Page 1 of the engineering process instruction templateFields for EPI number, revision, title, effective date, owner and what it applies to, boxes for purpose and scope and references, an equipment and materials table and a process parameters table with nominal, lower and upper limits.
Purpose and scopeReferencesEquipment and materialsParameters and limitsProcess sequenceValidation or qualificationAcceptance criteriaChange history and approvals

When to use it

When to use an engineering process instruction

  • For special processes such as heat treatment, welding, plating, bonding or molding, where the result depends on the process window.
  • When a process is introduced, moved to a new line or site, or given new equipment.
  • When process limits need to be agreed and documented before work instructions are written.
  • When a customer or your quality system asks for the process to be defined and validated.

How to fill it in

  1. 1

    Define the scope

    What the process does, which parts, lines and sites it covers, and what it does not cover.

  2. 2

    List the references

    Drawings, material and process specifications, customer requirements, the FMEA and the control plan.

  3. 3

    Set the parameters and limits

    For each parameter: the unit, nominal, lower and upper limit, how it is set and monitored, how often, and what to do if it goes out.

  4. 4

    Write the sequence

    The main stages of the process in order. The detail for operators goes in the work instructions.

  5. 5

    Validate the process

    Record how the equipment, the parameter window and the output were proven before production, with the method, acceptance criterion and result.

  6. 6

    Approve and control changes

    Engineering, quality, production and EHS sign. For every change, record whether it needs revalidation and update the work instructions.

A filled-in example

Illustrative, not a benchmark

An example: an EPI for induction hardening a shaft (illustrative values).

The example's validated process window

  • Powertarget 85, 80 to 90 kW
  • Scan speedtarget 6, 5.5 to 6.5 mm/s
  • Quench concentrationtarget 8, 7 to 9 %
Parts were hardened at the low and high ends of the power and speed window and checked, so every setting inside these bands is proven.
  • Scope: induction hardening of the bearing journals on shafts in one part family, on one hardening machine.
  • Parameters: power 85 kW, 80 to 90; scan speed 6 mm/s, 5.5 to 6.5; quench flow 40 l/min minimum; quench concentration 8%, 7 to 9%.
  • Validation: parts hardened at the low and high ends of the power and speed window, cut and checked for case depth and hardness; all within the drawing requirement.
  • Acceptance criteria: surface hardness and case depth to the drawing, checked on the first and last part of each shift.

The station work instruction was written from the EPI, with the same limits, and a later change of quench fluid was recorded as needing revalidation before use.

Common mistakes

  • Limits with no reason

    Limits copied from an old document and never tested give false confidence. Base them on validation data.

  • Mixing it with the work instruction

    Operators need steps, engineers need the process definition. Keep the EPI for the definition and write the instructions from it.

  • No reaction plan

    Say what happens when a parameter goes out of its limits, including the parts made while it was out.

  • Changes without revalidation

    A new material, equipment or limit is a change to the process. Decide whether it needs revalidation before it is used.

Download the template

Free to use: print it, copy it and edit it for your team. Enter your name and work email once to download.

Run this template in LeanSuite

In LeanSuite an SOP can be drafted by AI from a video or a paper procedure, routed to engineering, EHS and quality for e-signature with an audit trail and version history, and kept in Document Management with an owner, a review date and read-and-sign.

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FAQ

Engineering process instruction (EPI) template: common questions

  1. The engineering definition of a process: its scope, equipment and materials, the parameters and their limits, how it was validated and what counts as an acceptable output. Work instructions for operators are written from it.

  2. An EPI defines the process for engineers. An MPI, or work instruction, tells the operator how to do the job at the station. The MPI should use the same limits as the EPI. Companies use the names differently, and no standard defines them.

  3. Each parameter that affects the result, with its unit, nominal value, lower and upper limits, how it is set and monitored, how often it is checked, and what to do if it goes out of limits.

  4. When something that affects the result changes: the equipment, a material, a parameter limit, the site or line. Decide it for each change and record the decision in the change history.

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