ForEach Array of Object in Angular

I have a problem in looping of quantity in my array of object since the quantity is inside of the array and it has its own array of object too. The problem is that the input box of the quantity is repeating twice. How can i get rid of the second input box of the quantity. Here's the link of my stackblitz LINK OF APP

 patchValues() {
    let rows = this.myForm.get('rows') as FormArray;
    this.orders.forEach(material => {
      material.materials.forEach(x => {
        rows.push(this.fb.group({
          material_id: x.id,
          material_name: x.name, 
          quantity: x.quantity.forEach(r => {
            rows.push(this.fb.group({
              quantity: r.qty
            }))
          })
      }))
    })
  })
}