Jobs › Flex

Plastic Molding Engineering Co-Op - Spring 2027

Flex · Libertyville, IL · $27.50–$44.50 an hour · Full time

Posted Sep 18, 2026 · We last checked this listing on Oct 6, 2026

Apply at Flex

Likely interview questions for this role

Written from this job description, not a generic list. Each one notes what the interviewer is really checking.

About your past

Tell me about a time you tracked down the root cause of a problem, in a lab, a project or a job.

What they are checking: Whether they dig past the first answer, which is how defect analysis is done well.

How careful are you with documentation? Tell me about a time accuracy in records mattered.

What they are checking: Whether they can keep the precise records that validation work on medical parts demands.

Tell me about a team you worked on where you had to learn from people more experienced than you.

What they are checking: Whether they can absorb guidance and work alongside engineers and technicians without needing constant direction.

What interests you about molding high-precision medical components specifically?

What they are checking: Whether they are drawn to this work for real reasons, which predicts how engaged they will be.

What would you do

You notice a defect during a trial that the engineer didn't mention. What do you do?

What they are checking: Whether they speak up about what they see, since a co-op's fresh eyes are useful only if they share them.

About the work

What do you know about how injection molding works, from resin to finished part?

What they are checking: Whether they understand the basic process well enough to contribute to mold trials from the first week.

What is a short-shot study, and what does it tell you about a mold?

What they are checking: Whether they grasp how fill studies reveal flow and imbalance problems, which is listed daily work.

If a multi-cavity mold is filling unevenly, what could cause that?

What they are checking: Whether they can reason about imbalance from runners, gates, temperature and tooling rather than guessing.

What do IQ, OQ and PQ mean, and why would a medical component maker care about them?

What they are checking: Whether they understand process validation and why regulated products require documented proof the process works.

What is a process window, and how would you help find one during a mold trial?

What they are checking: Whether they understand that a robust process makes good parts across a range of settings, not one magic point.

Practice this interview out loud.

Offer builds a real interview for this exact role at Flex from your resume and this job description, asks the questions one at a time, and tells you what landed. The first one is free.

Practice this out loud

The full job description

As published by Flex.

Flex is the diversified manufacturing partner of choice that helps market-leading brands design, build and deliver innovative products that improve the world. A career at Flex offers the opportunity to make a difference and invest in your growth in a respectful, inclusive, and collaborative environment. If you are excited about a role but don't meet every bullet point, we encourage you to apply and join us to create the extraordinary. Job Summary 

 To support our extraordinary teams who build great products and contribute to our growth, we’re looking to add a Plastic Molding Engineering Co-Op located in our Libertyville, IL site. Reporting to Process & Automation Engineering Team, the student will support injection molding process development and validation activities for high-precision medical components, while collaborating and working alongside Engineers and cross-functional teams. What a typical day looks like: • Assist in injection mold trials and process window development • Support startup optimization and parameter validation • Perform short-shot and imbalance studies • Support defect analysis and root cause investigations • Assist with IQ/OQ/PQ documentation • Support tooling PM and mold performance assessments • Attend team meetings to support project work as needed Student qualities we’re seeking for this Co-Op assignment: • Currently enrolled student pursuing MS/BS degree in Plastics Engineering, Polymer Engineering, Mechanical Engineering, or Materials Science major • Understanding of Injection Molding Process (injection molding fundamentals) • Basic process validation knowledge in highly regulated environments • Defect & root cause analysis experience • Understanding of mold tooling components and ability to read basic mechanical drawings • Strong documentation and communication skills • Previous manufacturing floor internship experience a plus! Co-Op Program Requirements: • Ability to work 40 hours/week (in person) during the Spring 2027 co-op assignment • Currently enrolled in accredited university • 3.0 GPA min 

 Application Deadline: Applications for this job position will be accepted for at least five days following the job posting start date below and continuing until the end date below or until the position is filled. This posting may close sooner due to application volume. Job Posting Start Date 09-18-2026 Job Posting End Date 09-25-2026

 The base pay range for this position is provided below. The final base rate offered will be determined using job-related, non-discriminatory criteria, including but not limited to experience, qualifications, geographic location, education, external market data, and internal equity. Pay Range $27.50 - $44.50 Hourly Job Category Intern Is Sponsorship Available? No Flex is an Equal Opportunity Employer and employment selection decisions are based on merit, qualifications, and abilities. We do not discriminate based on: age, race, religion, color, sex, national origin, marital status, sexual orientation, gender identity, veteran status, disability, pregnancy status, or any other status protected by law. We're happy to provide reasonable accommodations to those with a disability for assistance in the application process. Please email accessibility@flex.com and we'll discuss your specific situation and next steps (NOTE: this email does not accept or consider resumes or applications. This is only for disability assistance. To be considered for a position at Flex, you must complete the application process first).

Apply at Flex