Beginner’s Guide to Injection Molding: Easy Tips for Success

The Problem: Injection Molding Can Be Hard

Are you new to making plastic parts? Do you feel lost when you hear words like “sink marks” or “gate placement”? Many people find injection molding hard to learn. The machines are big. The terms are strange. The costs can be high. And if you make a mistake, you waste time and money. Did you know that 5-10% of all injection molded parts have flaws[^1]? These flaws can make your parts weak or ugly.

Why This Makes Things Worse

When your plastic parts have flaws:

• Your customers may not want them
• You lose money on parts you can’t use
• You fall behind on your work
• You have to start over and spend more A bad mold can cost you $1,000 to $100,000[^2] with no good parts to show for it!

The Solution: Istar Machining’s Expert CNC Services

At Istar Machining, we know how to make perfect molds for your plastic parts. Our CNC machining makes molds that give you great parts every time. Our team has made hundreds of molds for all kinds of parts. We can help you save money and make better products. Let’s learn the basics of injection molding so you can work with us to make amazing parts!

1. What is Injection Molding?

Injection molding is how we make plastic parts by putting hot plastic into a mold. The plastic gets cold and hard, and then we take out the new part. 

Main Uses for Injection Molding:

• Car parts (dash boards, door handles)
• Toys (like LEGO bricks)
• Home items (cups, storage bins)
• Medical tools (syringes, cases)

Why People Like Injection Molding:

• Make lots of parts fast
• All parts look the same
• Can make complex shapes
• Works with many types of plastic

2. The Injection Molding Process in 4 Steps

The process is easy to understand but needs skill to do well. 

Step 1: Clamping

The mold has two parts that must stay closed tight. The machine holds them with a strong clamp.

Step 2: Injection

The machine melts plastic pellets and pushes the hot plastic into the mold. This happens fast – often in less than 1 second!

Step 3: Cooling

The hot plastic cools down and gets hard. This can take from 15 to 60 seconds[^3] based on how big and thick your part is.

Step 4: Ejection

When the part is hard, the mold opens and small pins push the part out. At Istar Machining, we use 5-axis machining to make molds with perfect shapes and smooth surfaces.

3. Choosing the Right Material

Not all plastics work the same way! Here’s a table showing the main types:

We help you pick the best plastic for your part based on:

• How it will be used
• What heat it might face
• If it needs to be strong
• If it needs to be food safe Our CNC plastic work makes molds that work great with all these materials!

4. Critical Design Rules for Good Parts

Good design is key to making good parts. Here are the most important rules: 

Wall Thickness

• Keep walls the same thickness
• Most parts work best with walls 2-3mm thick
• Thin spots cool fast, thick spots cool slow (makes warping)

Draft Angles

• Add a slight slope (1-2°) on walls
• This helps the part come out of the mold
• No draft = parts get stuck

Ribs and Supports

• Add ribs to make parts strong without using too much plastic
• Make ribs 60% as thick as walls
• Space them well to avoid sink marks

Gate Placement

• The gate is where plastic goes into the mold
• Put gates where marks won’t show
• Good gates mean better flow and fewer problems At Istar Machining, our design for CNC machining team can help make your design better for molding.

5. Common Problems & How to Fix Them

Even with good design, things can go wrong. Here are the main problems and how to fix them: 

Sink Marks

PROBLEM: Dents in thick parts of the plastic FIX:

• Make walls more even
• Add cooling where needed
• Use 5-axis machining for better mold cooling lines

Flash

PROBLEM: Thin bits of extra plastic at the edges FIX:

• Use more clamp force
• Check that mold parts fit well
• We can make molds with tight fits using precision CNC machining

Warping

PROBLEM: Parts bend as they cool FIX:

• Make better cooling in the mold
• Use plastic that shrinks less (like ABS)
• Our CNC milling makes cooling lines that reach all parts of the mold

Short Shots

PROBLEM: Parts don’t fill all the way FIX:

• Make the plastic hotter
• Inject faster
• Make gates bigger Istar Machining’s custom CNC machining can fix these issues in your molds.

6. Types of Injection Molding

There are special types of injection molding for different needs: 

Overmolding

This puts a soft layer over a hard part (like rubber grips on tools).

Insert Molding

This puts metal parts inside the plastic (like threads in a plastic cap).

Micro Molding

This makes tiny parts (like gears for watches). All these types need special molds that we can make with our CNC machining service.

7. How Much Does Injection Molding Cost?

The cost has two main parts:

Mold Cost

• Simple molds: $1,000-$5,000
• Complex molds: $10,000-$100,000+
• The mold is a one-time cost

Part Cost

• Small runs (100-1,000): $1-10 per part
• Big runs (10,000+): $0.50-5 per part
• The more you make, the less each part costs CASE STUDY: A car dash maker saved $50,000 a year[^4] by fixing sink marks with better mold cooling channels made with CNC machining!

8. Real Examples of Injection Molding Success

These real stories show how good injection molding helps make great products:

LEGO Bricks

• Make 36,000 bricks every minute
• Parts fit with less than 0.005mm difference
• Use multi-cavity molds and fast ejection[^5]

Medical Syringes

• Need to be clean and clear
• Use PC (polycarbonate) plastic
• Made with 99.9% good parts[^6]

Car Dashboards

• Use ABS plastic with even 2.5mm walls
• Have many cooling lines
• Get 30% fewer flaws than old designs[^7]

9. How Istar Machining Can Help You

At Istar Machining, we make perfect molds with our CNC machines. Here’s how we help: 

Design Help

We check your designs for:

• Wall thickness
• Draft angles
• Cooling lines
• Gate spots

Perfect Molds

Our precision CNC machining makes molds with:

• Smooth surfaces
• Exact sizes
• Perfect fits
• Great cooling

Testing

We can help test your mold with:

• Small runs first
• Flow testing
• Fixing any issues

Materials

We can make molds from:

• Steel for long runs
• Aluminum for fast, low-cost molds
• Special metals for tough plastics

10. Next Steps to Start Your Project

Ready to make your plastic parts? Here’s how to start:

1. Call us to talk about your part
2. Send us your design files
3. We’ll check for any issues
4. We’ll give you a price and time
5. We make your mold with our CNC machines
6. We test the mold and make fixes if needed
7. You get perfect parts!

FAQs About Injection Molding

Conclusion: Start Making Better Parts Today

Injection molding can be easy when you work with experts. At Istar Machining, we help you:

• Make better mold designs
• Get perfect molds from our CNC machines
• Fix problems before they cost you money
• Make parts that make your customers happy Don’t let injection molding problems hurt your business. Our CNC machining service makes molds that give you the edge over your competition. Call us today to talk about your next injection molding project!